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As the integration of renewable energy sources into the grid intensifies, the efficiency of Battery Energy Storage Systems (BESSs), particularly the energy efficiency of the ubiquitous lithium-ion batteries t.
Charge discharge efficiency in lithium-ion batteries is influenced by a multitude of factors, including the battery's internal chemistry, the operational environment, and the charging/discharging protocols employed. Temperature Impact: Temperature significantly influences charge discharge efficiency lithium ion batteries.
Efficient charging reduces heat generation, which can degrade battery components over time, thus prolonging the battery's life. Several factors influence the charging efficiency of lithium ion batteries. Understanding these can help in optimizing charging strategies and extending battery life.
The expanding use of lithium-ion batteries in electric vehicles and other industries has accelerated the need for new efficient charging strategies to enhance the speed and reliability of the charging process without decaying battery performance indices.
However, a battery pack with such a design typically encounter charge imbalance among its cells, which restricts the charging and discharging process . Positively, a lithium-ion pack can be outfitted with a battery management system (BMS) that supervises the batteries' smooth work and optimizes their operation .
Therefore, even if lithium-ion battery has a high CE, it may not be energy efficient. Energy efficiency, on the other hand, directly evaluates the ratio between the energy used during charging and the energy released during discharging, and is affected by various factors.
Discharging a lithium-ion battery allows it to supply power to devices. This process moves lithium ions and generates an electric current. Proper discharge management ensures efficiency, extends battery life, and prevents damage. How Does Discharging a Lithium-Ion Battery Work?
A system combination of small wind turbines, solar panels and battery storage units can generate the required electricity on site to support the UPS independently of the grid.
Guide for Batteries for Uninterruptible Power Supply (UPS) Systems. Guide for making informed decisions on selection, installation design, installation, maintenance, and testing of VLA, VRLA and Ni-Cd stationary standby batteries used in UPS systems.
Recently, a client approached us needing new UPS systems for both their offshore platforms and their onshore substations for a brand new offshore wind farm energy and power project.
UPS batteries should never be installed outdoors where they can be exposed to the damaging effects of sunlight. IEEE 1635/ASHRAE 21 is a good engineering reference for designing properly ventilated battery rooms and cabinets. Lead-acid batteries contain substances that are not good for the environment in which we live.
The UPS and/or battery cabinets might be configured to look like standard computer equipment racks. There are two primary hazards of concern: electrical and fire. Open rack batteries expose potentially lethal voltage to any person coming in contact with them.
Of the three main subsystems, the battery is what makes the system “uninterruptible”. Depending upon the system design, the battery can constitute as much as 50% of the cost of the UPS. Without a reliable battery, the operation of the entire data center can be put at risk.
Smaller UPS systems (e.g, up to 250 kVA) are commonly installed directly in the computer room along with their respective battery cabinets. The UPS and/or battery cabinets might be configured to look like standard computer equipment racks. There are two primary hazards of concern: electrical and fire.
A lithium-ion battery can store an average of 150 to 250 watt-hours per kilogram (Wh/kg) of energy. This value varies based on the battery's chemistry, design, and intended application.
This does not directly tell you how much energy the battery can store, but can be a more useful value in deciding how long a circuit will run from a battery. For example, a car battery might be rated for 50 Ah. That means in theory it could source 50 A continously for 1 hour and then go dead.
Lithium-ion batteries are used a lot because of their high energy density. They're in electric cars, phones, and other devices that need a lot of power. As battery tech gets better, we'll see even more improvements in energy storage capacity and volumetric energy density. The journey of battery innovation is amazing.
Lithium Iron Phosphate (LFP): LFP batteries hold 90 to 160 Wh/kg. They're safe and last a long time. They're good for tools and storing energy. Lithium-ion batteries have gotten better over time. They've gone from 80 Wh/kg in the 1990s to over 300 Wh/kg now. Scientists have even made them better, up to 700 Wh/kg.
Batteries store energy through electrochemical storage. This means chemical reactions turn electrical energy into stored energy. When charged, these reactions reverse, letting the battery release energy. This cycle makes batteries very useful. Specific energy (Wh/kg) – The energy a battery can store per unit of mass.
In 2010, lithium-ion batteries cost over $1,000/kWh. Now, they're under $200/kWh. Prices are expected to keep falling, making electric vehicles and renewable energy storage more affordable. Explore my comprehensive Battery Energy Density Chart comparing different power storage solutions.
Specific energy (Wh/kg) – The energy a battery can store per unit of mass. Energy density (Wh/L) – The energy a battery can store per unit of volume. Power density (W/kg) – The power a battery can deliver per unit of mass. Cycle life – The number of charge/discharge cycles a battery can handle before it loses a lot of capacity.
Equipment and Materials shall be new and unused. Battery rack and Equipment shall be in accordance with the Saudi Aramco-approved project-specific design drawings, diagrams, schedules, lists, databases, and associated design documents. “For Valve Regulated Batteries: a) Rack Construction The modular battery rack shall be welded steel units containing a maximum of 6 cells per unit. Each module shall be designed to allow.
Battery energy storage system specifications should be based on technical specification as stated in the manufacturer documentation. Compare site energy generation (if applicable), and energy usage patterns to show the impact of the battery energy storage system on customer energy usage. The impact may include but is not limited to:
Any customer obligations required for the battery energy storage system to be installed/operated such as maintaining an internet connection for remote monitoring of system performance or ensuring unobstructed access to the battery energy storage system for emergency situations. A copy of the product brochure/data sheet.
Standard battery rack as specified in Sec. 11.1.1 shall be acceptable as well since it facilitates removal and/or installation of batteries. “Stack Height The vertically stacked height of valve regulated batteries shall not exceed 1700 mm above the floor. VRLA battery mounting on a standard rack shall be allowed with its shall not exceed 1700mm.
Any upgrades to existing site electrical infrastructure required to install proposed battery energy storage system. All components of the system should be suitable for installation under Australian legislation and Standards.
Any bollards required to be installed in front of battery energy storage system. Safety exclusion zone around battery energy storage system if required. Location of main switchboard. Any other existing NET on site.
and are responsi-ble for connecting/disconnecting individual racks from the system. A typical lithium-ion (li-ion) rack cabinet configura-ti comprises several battery modules with a dedi-cated battery energy management system. The most commonly used batteries in energy stor-age installations are li-ion batteries;
Solar panels, also known as photovoltaics (PV) panels, capture energy from sunlight that you can use to charge your electric vehicle. Depending on how much energy your solar panels generate, you can pote. Solar panel charging is easy to wrap your head around. 1. Your solar panels convert sunlight into DC electricity 2. An inverter, part of your solar system, converts that DC electricity to AC electricity 3. The AC electricity is fed t. You don't need special solar panels for EV charging. Normal solar panels will do. The most important thing is the energy they can generate as a system and the predicted energy they will generate when it's cloudy. Solar installation. What to do with all the energy you don't use? You can store it in an energy storage system, a giant battery that captures electricity for you. An energy storage system lets you charge with solar power at night because it. Once you have your solar system, you need a solar-integrated smart charger. A solar integrated smart charger basically has terminals for a solar or renewable feed, creating a connection between your solar system and EV c.
[PDF Version]Using solar panels to charge an electric car can reduce carbon emissions and save the average household over £400 a year. Solar panels offer homeowners a way of generating clean, renewable energy to power their homes. So can they also charge our electric vehicles? In short, yes!
On average, you need six solar panels to charge an electric car – assuming each panel has a peak rating of 400W. However, the average three-bedroom household that's looking to power its appliances and charge an EV will need a 5.9kWp system, which is 14 solar panels at 400W each.
Battery charging from solar panels is a renewable and sustainable way to power your electric vehicle. Simply put, solar panels work by converting sunlight into electricity, which can then be used to charge your EV battery.
With a small setup like this, you can either charge your EV slowly with 100% solar or supplement grid energy with solar energy to slash your charging costs. You need only two things to charge your EV with solar panels: a solar system and a smart home charger with solar integration. These are the best chargers with solar we've reviewed:
Solar panels are rarely used to fully power an EV, but they can top up its charge After paying the installation costs of an electric charger, you're also faced with the price of the electricity to charge your car. You can reduce this with solar panels, leaving you with a smaller carbon footprint and more money in the bank.
Each solar panel in a solar PV system will typically produce about 355W of energy in conditions of strong sunlight. So you'll get about 30 miles of driving for each hour of charging with our 7.4kW charger. The amount of solar energy that may be used to charge an electric vehicle will, of course, vary depending on the season and the weather.
Most of the BESS systems are composed of securely sealed, which are electronically monitored and replaced once their performance falls below a given threshold. Batteries suffer from cycle ageing, or deterioration caused by charge–discharge cycles. This deterioration is generally higher at and higher. This aging cause a loss of performance (capacity or voltage decrease), overheating, and may eventually le.
Battery Energy Storage Systems function by capturing and storing energy produced from various sources, whether it's a traditional power grid, a solar power array, or a wind turbine. The energy is stored in batteries and can later be released, offering a buffer that helps balance demand and supply.
In the transition towards a more sustainable and resilient energy system, battery energy storage is emerging as a critical technology. Battery energy storage enables the storage of electrical energy generated at one time to be used at a later time. This simple yet transformative capability is increasingly significant.
The components of a battery energy storage system generally include a battery system, power conversion system or inverter, battery management system, environmental controls, a controller and safety equipment such as fire suppression, sensors and alarms. For several reasons, battery storage is vital in the energy mix.
They make renewable energy more reliable and thus more viable. The supply of solar and wind power can fluctuate, so battery storage systems are crucial to “smoothing out” this flow to provide a continuous power supply of energy when it's needed around the clock, no matter whether the wind is blowing or the sun is shining.
Energy can be stored in batteries for when it is needed. The battery energy storage system (BESS) is an advanced technological solution that allows energy storage in multiple ways for later use.
On a more localized level, a BESS allows homes and businesses with solar panels to store excess energy for use when the sun isn't shining. Using a battery energy storage system in this way increases energy independence. It reduces reliance on the grid, reducing emissions associated with energy production and transmission.
Up to 43% of total energy consumption in the battery manufacturing process is used to keep the dry rooms super dry — that's a relative humidity of below 1% and dew points ranging from -40°C to -120°C.
As gas enters the battery system interior, humidity can also enter. If the surface temperature of e.g. cooling plates falls below the dew point, condensation on those cold surfaces inside the system will occur. So an additional device is required to prevent condensation. 3. Humidity control
thermal management of batteries in stationary installations. The purpose of the document is to build a bridge betwe the battery system designer and ventilation system designer. As such, it provides information on battery performance characteristics that are influenced by th
of developing a joint standard on battery room ventilation. For ASHRAE the goal was to reduce the energy consumption that results from traditional battery room ventilation systems where al
3. Humidity control To reduce the system complexity, two important functions – pressure balancing and emergency degassing – are com-bined into one unit. The unit has to ensure that no liquid water can enter the battery housing under all conditions. A PTFE membrane was validated for this application.
Operation in hot, humid climates will pose the greatest challenge as the air entering the HV battery system will carry more water vapor, thus increasing the absolute humidity inside the system. As eficient battery cooling is also required especially under these conditions, the risk of water condensation is especially high.
During the ESS operation period, the indoor temperature was maintained within 20–20.9 °C, and the indoor humidity was maintained at 50.2–82.3%, while the outdoor temperature was in the range of 27.7–32.3 °C, and outdoor humidity was in the range of 56.6–79.5%. High indoor humidity may corrode the battery and reduce its lifecycle. Figure 9.
A battery energy storage system (BESS), battery storage power station, battery energy grid storage (BEGS) or battery grid storage is a type of technology that uses a group of in the grid to store. Battery storage is the fastest responding on, and it is used to stabilise those grids, as battery storage can transition fr.
A battery energy storage system (BESS) is an electrochemical device that charges (or collects energy) from the grid or a power plant and then discharges that energy at a later time to provide electricity or other grid services when needed.
Secondary energy storage in a power system is any installation or method, usually subject to independent control, with the help of which it is possible to store energy, generated in the power system, keep it stored and use it in the power system when necessary.
In the quest for a resilient and efficient power grid, Battery Energy Storage Systems (BESS) have emerged as a transformative solution. This technical article explores the diverse applications of BESS within the grid, highlighting the critical technical considerations that enable these systems to enhance overall grid performance and reliability.
The other primary element of a BESS is an energy management system (EMS) to coordinate the control and operation of all components in the system. For a battery energy storage system to be intelligently designed, both power in megawatt (MW) or kilowatt (kW) and energy in megawatt-hour (MWh) or kilowatt-hour (kWh) ratings need to be specified.
The third part which is about Power system considerations for energy storage covers Integration of energy storage systems; Effect of energy storage on transient regimes in the power system; and Optimising regimes for energy storage in a power system.
By placing energy storage systems where they are most needed, grid operators can ensure more efficient voltage regulation, especially in areas with high load density or regions far from traditional generation sources. The Power Conversion System (PCS) within the BESS plays a crucial role in providing voltage support.
The BPS enclosure has mounting brackets for up to three Signa-ture modules to the right of the circuit board. anywhere on a notification appliance circuit NAC Circuit NAC To next signaling Circuit Existing NAC end-of-line resistors are not required to be installed at the booster's terminals. This allows multiple boosters to be driven from a single NAC circuit without the need for.
A battery booster operates by providing a surge of electrical power to a vehicle's battery, enabling it to start when it lacks sufficient charge. This device typically includes a rechargeable battery, jumper cables with clamps for connection, and safety features to prevent damage during use. Components and Operation of Battery Boosters:
Lithium-ion booster packs: Use a lithium-ion battery as their power source, similar to the one on your cell phone. They are generally smaller and lighter than lead-acid booster packs but do not be fooled by their compact size, lithium-ion booster packs can give you as much cranking power as lead-acid booster packs.
Battery Boosters, or Booster-packs are essentially a portable car battery. They provide high amperage (800-1200 amps) power through connector clamps, and can start a vehicle with or without a battery. Most standard jump packs are about a cubic foot in size, have a carry handle, and many can be rather heavy as they are housing a heavy duty battery.
The Booster Power Supply (BPS) is a UL 864, 10th Edition listed power supply. It is a 24 Vdc filtered-regulated, and supervised unit that can easily be configured to provide additional notification appliance circuits (NACs) or auxiliary power for Mass Notification/ Emergency Communication (MNEC), as well as life safety applications.
Versatile Applications: They are handy for camping trips, outdoor activities, and road trips, providing a reliable backup power source. Commercial and Industrial Use: Larger battery boosters are used in commercial settings, such as automotive repair shops and construction sites, to maintain vehicle fleets and heavy machinery.
When your battery is completely dead and you need immediate power, a boost charger (also known as a jump starter) delivers a quick, high-amp charge to get the car started quickly. However, it's not intended for long-term charging or battery maintenance. 1. Battery Chargers
Most homeowners with solar on their homes have what is called a “grid-tied” solar system, which means the panels are connected to an inverter. The inverter is connected to the main AC panel in the house and to a special smart electric meter that records both energy you use from the utility company and energy. If you want to keep your home up and running when the power goes out, there are a few ways to do so: 1. Use a backup gas generator 2. Add solar. Since solar panels depend on the sun they won't be much good at night and will produce less energy depending on the season. Luckily, there two. The reliability and lifespan of solar panels is excellent, according to a recent studyby NREL. The researchers looked at 54,500 panels installed between. People who want to get off fossil fuels completely and ensure that only clean energy passes through their wires might be tempted to go off-grid completely. And that certainly is an option, but it can be a very costly one. Though going solar has never been less expensive.
[PDF Version]Adjusting your batteries so they provide power any time your solar panels do not meet your energy needs. Customizing your battery distribution to supplement your electricity during peak hours to reduce typical utility bills. Where Can I Get a Battery Backup?
If you run an off-grid system, it's a good idea to have some simple backup devices like flashlights, emergency lights, and portable gas heaters. If your off-grid solar system regularly runs out of power, then either you don't have enough solar panels or you don't have enough battery storage to meet your energy needs.
During a power outage, solar panels require batteries for energy storage to function effectively. Without a battery backup system, solar panels alone can't power your home during outages. The energy storage system is the key to guaranteeing continuous power supply from your solar power system.
You can tap into stored solar power during a power failure. Some home battery systems, such as the Panasonic EVERVOLT, even enable you to keep your solar panels running throughout a grid failure so they can keep recharging your battery. What happens to a battery system during a power outage?
Keeping your battery in working mode to only dispense power during an outage. Adjusting your batteries so they provide power any time your solar panels do not meet your energy needs. Customizing your battery distribution to supplement your electricity during peak hours to reduce typical utility bills.
With this system, your solar panels and batteries each have their own inverters. Within the panels the power is converted from DC to AC power, which you can use in your home. Then, in the battery, the power is inverted back to DC power for storage.
You have a couple of recharging solutions to consider should your electric car run out of battery: If it is not possible to recharge at a nearby charging station then you can use a portable charger or call for a breakdown cover provider who will charge the EV with a partial charge or tow you to a charging station. Here's a. So, power is starting to run out or you've come to a complete stop, let's look at your options: 1. Find a nearby charging station Yep – captain obvious. The most common-sense answer is. Most EVs provide real-time information about the battery's state of charge, so it's really easy for drivers to see how low the battery is getting. Here are. Try to keep calm, this is stressful but panicking can make the situation worse. As soon as you notice your battery is running critically low or the car starts to lose power you should pull over safely onto the hard shoulder or. An electric car could potentially travel for around 10-40 miles on a low battery before running out of power (estimated for a battery of around 10%.
[PDF Version]You have a couple of recharging solutions to consider should your electric car run out of battery: If it is not possible to recharge at a nearby charging station then you can use a portable charger or call for a breakdown cover provider who will charge the EV with a partial charge or tow you to a charging station.
The best way to avoid running out of battery is to ensure you're never in that position; this is much easier nowadays with improved EVs. Be careful not to charge your EV to 100% too often or drain it to 0%, as doing either can damage your battery condition, limiting your battery life and range.
As soon as you notice your battery is running critically low or the car starts to lose power you should pull over safely onto the hard shoulder or the nearest safe area away from the traffic. Turn on your hazard lights to alert other drivers and place a warning triangle at a safe distance behind the car.
On the off chance you do run out of electricity, contact your breakdown provider. It may have a small battery booster that can give you enough charge to get to a charging station. If not, ask for a flatbed truck to take you to a nearby charging station.
When an electric car runs out of battery the power to the electric motor will eventually stop. The electric motor is pretty important, as you can imagine, it makes the vehicle drive! So the car will gradually lose speed and eventually come to a complete stop.
If you run out of battery power, there is less of a chance you'll damage your EV's powertrain than if you were to starve an internal combustion engine of fuel. For instance, EVs don't have a fuel pump or fuel filter that can be damaged by running the engine with an empty fuel tank. An EV will simply slow down and, eventually, completely shut down.
What is the Function of a Charger Module?Charging the Rechargeable Batteries The primary function of charger modules is to charge rechargeable batteries. Stabilizing the Flow of Current. Protection from Overcharging and Drainage.
This module is made for charging rechargeable lithium batteries using the constant-current/constant-voltage (CC/CV) charging method. In addition to safely charging a lithium battery the module also provides necessary protection required by lithium batteries. See below concerning the protection features this module provides.
Charger module for 3.7V lithium power (LiPo) packs which do not include their own protection circuit. Feeds a 1A charge current to the battery and cuts off when a full charge is detected (4.2V). Input is 5V via a micro-USB connector or +/- solder connections. The battery should be connected to the B+/B- terminals.
TP5100 Charging Module Pinout, Alternative, Circuit, and Specs. The TP5100 is an integrated Lithium battery charger that has a switch mode buck topology. It has all the integrated functions to charge a single or dual cell Lithium battery, along with a few peripheral components. Input voltage pin (20V max.) TP4056, TP5000 Related Components
Input is 5V via a micro-USB connector or +/- solder connections. The battery should be connected to the B+/B- terminals. A load can be connected to the OUT+/OUT- terminals, but should be disconnected during charging. The module provides load cut-off when the battery voltage falls to 2.4V.
Feeds a 1A charge current to the battery and cuts off when a full charge is detected (4.2V). Input is 5V via a micro-USB connector or +/- solder connections. The battery should be connected to the B+/B- terminals. A load can be connected to the OUT+/OUT- terminals, but should be disconnected during charging.
It is always good to be careful while working with Lithium batteries. The module operates with 5V which can be provided by the USB mini cable that is commonly used for charging smartphone. You can use any type of mobile charger and its cable to power this module.
Charging Procedure: Step-by-Step1. Set Voltage and Current Voltage Setting: Adjust the power supply to the desired voltage before making any connections to the battery.
A home battery storage system which can charge from the grid is a feasible means of getting around this issue. In short, you have the benefits of cheaper (and generally greener electricity) without the inconvenience of shifting energy usage to different times of the day. 2. Smart time-of-use tariffs
It's also possible to charge your home battery storage with off-peak electricity. There are still Economy 7 tariffs available with a cheap night rate. There are also many other modern tariffs available, designed for customers with solar panels, electric cars, and batteries.
Using your EV charger with your home battery storage system allows you to charge your car strategically, e.g. when your battery is fully charged or when you're generating renewable energy. One more thing
GivEnergy home batteries will charge and discharge intelligently by default, taking advantage of cheaper energy rates. However, you can also take a more hands-on approach by setting schedules and timers around your energy usage and lifestyle. You can do this through the energy monitoring software: portal and app.
As mentioned above, you can charge your battery strategically. GivEnergy home batteries will charge and discharge intelligently by default, taking advantage of cheaper energy rates. However, you can also take a more hands-on approach by setting schedules and timers around your energy usage and lifestyle.
Let's start with the battery – the muscle behind your home battery storage system. The size of the battery you install depends on your energy needs. A detached house with five people will likely use more energy than a small 1-bedroom flat with two people. Make sure you do your research before choosing a home battery that's right for you.
As a rule of thumb, if you motor for five hours or more a day at medium speed, you should – depending on the technical equipment of the yacht – have charged your batteries sufficiently (with about 250 amps, depending on the engine/alternator and batteries) to be able to use normal consumers on board for a while. In. This could look like this: when the yacht is disconnected from shore power, after about ten to 15 minutes the voltage/volt of the consumer battery should be read and noted. Depending on the battery type, this voltage/volt may be. By the way, the lion's share of electricity consumption on the yacht is usually the refrigerator. The consumes on average about 100 watts (eight. Here are a few rough guide values for orientation: 1. Refrigerator per day about 120 amps 2. Pressurized water pump per person per 24 hours about ten amps 3. Electric toilet per person. In the evening before going to bed should be fully charged again. Typically, the engine or power generator is then charged in the morning until the consumption of the previous night is compensated. If the voltage drops to such a.
[PDF Version]Battery Charging On Board Ship. Batteries are one of the energy sources available on board vessels which are used in case of blackout and emergency situations on board a ship.
As a rule of thumb, if you motor for five hours or more a day at medium speed, you should – depending on the technical equipment of the yacht – have charged your batteries sufficiently (with about 250 amps, depending on the engine/alternator and batteries) to be able to use normal consumers on board for a while.
If properly calibrated, the battery 12.9V full charge. 12.5V 75 per cent charge. 12.2V 50 per cent charge. 12.0V 20 per cent charge. 11.8V battery flat. A slightly larger panel, connected via a regulator, will also replenish the batteries while the boat is not being used, such that each time you arrive at the boat they are already fully charged.
You have about 1/2 understanding of an on-board charger. An onboard charger is nothing more than a 1 bank (one battery), 2 bank (two batteries), or 3 bank (three battery) charger. It does not connect to the engine! It is powered by 120 volts AC power from a standard household outlet when at the dock or at home.
Depending on the battery type, this voltage/volt may be between 12.2 to 14.4 volts – value of the “full charge” of the batteries. After an hour of sailing or a swim stop, the voltage should be checked again to correctly estimate the voltage loss.
This voltage is about 14.4V for a low maintenance battery and 15.2V for a standard battery. The voltages are chosen to enable a full charge without significant gassing. Normally there is a selector switch so you can set the charger according to the type of battery.
Yes, you can charge a lithium-ion battery from two sources. Both sources must have the same voltage to work together. One charger will provide most of the current, while the other may stop.
You could use a power supply with a higher voltage than the battery, both the battery and the power supply have their own diode feeding the Arduino. As long as the mains are good the higher voltage will block the current from the battery. When the mains fail the battery will have a higher voltage and provide power through its diode.
With mains present, the DC supply will maintain/charge the battery and power connected peripherals at the same time. You need to regulate the DC supply output voltage to match the battery maintenance-charge level (about 13.7V). At this level, you can leave it connected/powered at all times. Switchover is instant as this is a hot standby connection.
A relay will have some switching time with no power output. You could use a power supply with a higher voltage than the battery, both the battery and the power supply have their own diode feeding the Arduino. As long as the mains are good the higher voltage will block the current from the battery.
The common solution to this challenge is to use the mains regulated DC supply as a battery charger. With mains present, the DC supply will maintain/charge the battery and power connected peripherals at the same time. You need to regulate the DC supply output voltage to match the battery maintenance-charge level (about 13.7V).
Unless both devices are tied to the power connection you will have a problem if the mains power fails. A relay will have some switching time with no power output. You could use a power supply with a higher voltage than the battery, both the battery and the power supply have their own diode feeding the Arduino.
Many setups require two or more power sources and there can be problems when switching between them. For example, almost all portable electronic devices have integrated rechargeable batteries and a USB port for charging. This requires a solution for seamlessly transitioning between the internal battery and the external power sources.