What Is The Difference Between Alkaline And Other

What is the difference between Power Battery and energy storage battery?

1. The difference between the capacity of power battery and energy storage battery In the case of all new batteries, the battery capacity is tested by a discharge meter. Generally, the capacity of power lithium battery is about 1000-1500mAh; the capacity of energy storage lithium battery pack is above 2000mAh, and some can reach 3400mAh. 2.

What is the capacity of a lithium battery?

In the case of all new batteries, the battery capacity is tested by a discharge meter. Generally, the capacity of power lithium battery is about 1000-1500mAh; the capacity of energy storage lithium battery pack is above 2000mAh, and some can reach 3400mAh. 2. Different application industries of power batteries and energy storage batteries

What are power lithium batteries?

Power lithium batteries with different properties refer to batteries that provide power for transportation vehicles, generally compared with small batteries that provide energy for portable electronic devices; ordinary energy storage lithium batteries are a kind of lithium metal or lithium alloy as the positive electrode material.

How do energy storage batteries work?

In the energy storage system, the energy storage lithium battery only interacts with the energy storage converter at high voltage, and the converter takes electricity from the AC grid to charge the battery pack; or the battery pack supplies power to the converter, and the electrical energy is supplied by the converter.

What is the difference between wind power and solar power?

Wind power harnesses the energy from the wind to generate electricity. Wind turbines spin in the wind, which turns a generator to produce power. Solar power captures energy from sunlight using photovoltaic cells, converting it into electricity. Solar panels are commonly used on rooftops or in solar farms. 2. Energy Generation Process and Efficiency

Are solar energy storage systems a combination of battery storage and V2G?

This study proposed small-scale and large-scale solar energy, wind power and energy storage system. Energy storage is a combination of battery storage and V2G battery storage. These storages are in parallel supporting each other.

What is solar energy & wind power supply?

Solar energy and wind power supply are renewable, decentralised and intermittent electrical power supply methods that require energy storage. Integrating this renewable energy supply to the electrical power grid may reduce the demand for centralised production, making renewable energy systems more easily available to remote regions.

How is energy storage integrated into a power system?

To provide a stable and continuous electricity supply, energy storage is integrated into the power system. By means of technology development, the combination of solar energy, wind power and energy storage solutions are under development .

What are the benefits of solar energy & wind power?

By means of technology development, the combination of solar energy, wind power and energy storage solutions are under development . The solar and wind distributed generation systems have the benefits of the clean and renewable source of power supply.

Is solar energy efficient?

So, with PV, only a small number of energy can be converted into power — around 14% to 22%. In other words, yes, generally speaking, solar energy is pretty efficient. But that would depend on the system that you choose. As for wind energy, wind turbines can convert nearly half of the wind hitting them into electrical power.

What is the working principle of a lithium ion battery?

This means that during the charging and discharging process, the lithium ions move back and forth between the two electrodes of the battery, which is why the working principle of a lithium-ion battery is called the rocking chair principle. A battery typically consists of two electrodes, namely, anode and cathode.

What happens in a lithium-ion battery when charging?

What happens in a lithium-ion battery when charging (© 2019 Let's Talk Science based on an image by ser_igor via iStockphoto). When the battery is charging, the lithium ions flow from the cathode to the anode, and the electrons move from the anode to the cathode.

How does recharging a lithium ion battery work?

Here is the full reaction (left to right = discharging, right to left = charging): LiC 6 + CoO 2 ⇄ C 6 + LiCoO 2 How does recharging a lithium-ion battery work? When the lithium-ion battery in your mobile phone is powering it, positively charged lithium ions (Li+) move from the negative anode to the positive cathode.

How Lithium ion battery is charged and discharged?

The charging and discharging of lithium ion battery is actually the reciprocating motion process of lithium ions and electrons. When charging, apply power to the battery to let lithium ions and electrons go to the graphite layer along different paths. At this time, lithium atoms It is very unstable.

Why do lithium ion batteries need to be charged?

Simply storing lithium-ion batteries in the charged state also reduces their capacity (the amount of cyclable Li+) and increases the cell resistance (primarily due to the continuous growth of the solid electrolyte interface on the anode).

What is a lithium ion battery used for?

Lithium batteries are one of the best rechargeable batteries that can be used repeatedly. It has a wide range of applications, such as mobile phone batteries, power banks, and electric vehicle batteries. etc. So, how does the charging and discharging of lithium ion battery works?

What is battery acid made of?

The battery acid is made of sulfuric acid (H2So4) diluted with purified water to get an overall concentration of around 29-32, a density of 1.25-1.28 kg/L, and a concentration of 4.2 mol/L. The pH value of electrolytes is about 0.8, so we need to take utmost care when handling battery acid. What Is Battery Acid?

Why do batteries contain acid?

Batteries contain acid because it's fundamental to the electrochemical reaction that takes place. Also referred to as battery electrolyte, battery acid is the medium that carries the electrical flow between positive and negative electrodes.

What is car battery acid?

Car battery acid is around 35% sulfuric acid in water. Battery acid is a solution of sulfuric acid (H 2 SO 4) in water that serves as the conductive medium within batteries. It facilitates the exchange of ions between the battery's anode and cathode, allowing for energy storage and discharge.

What is the chemical formula for battery acid?

Battery acid primarily refers to sulfuric acid, with the chemical formula H2SO4. Now, if we break that down, we get two hydrogen atoms, one sulfur atom, and four oxygen atoms working together in harmony to perform a critical role in the battery's operations. Think of it as the fuel that powers the entire battery system. Why Sulfuric Acid?

What is battery acid used for?

Battery acid (AKA sulfuric acid) is used in lead-acid batteries to help create and store electrical energy, which powers many devices and vehicles.

Are acid batteries corrosive?

These batteries are highly corrosive, and react vigorously with the skin, causing burns and irritation. Battery acids have a high electrical conductivity. Usually, these acids are colorless. However, they can easily pick on impurities. The density of an acid battery is twice that of water.

Where can I test a solar PV system?

The test facilities are available at ERTL (East) Kolkata, ETDC Bengaluru, and some more laboratories. Products tested include Solar PV based Systems especially PV Lighting Systems, Solar Lanterns, Batteries, etc. Solar PV Testing - Overview:The use of solar and Photo Voltaic appliances is increasing in day-to-day applications.

How do you test a solar cell?

A Kelvin or four-wire measurement is essential to getting accurate IV data while testing a solar cell. A variable load is applied across the four wires in order to get a variety of current and voltage measurements for the device under test. Exactly what current and voltage is unknown until tested, which is why there is some iteration needed.

How often should a solar PV system be tested?

A solar photovoltaic (PV) system is required to be rigorously tested as part of the commissioning process and periodically throughout its subsequent lifespan. This is to test both the quality of the installation and the quality of its performance.

Why do solar panels need to be tested?

So continuously verifying system performance is essential. But the priority is safety, and because the panels are connected to the electricity grid and generate electricity themselves, maintaining the safety of the system is also essential and strictly regulated. What are the two types of solar PV testing?

What products are tested?

Products tested include Solar PV based Systems especially PV Lighting Systems, Solar Lanterns, Batteries, etc. Solar PV Testing - Overview:The use of solar and Photo Voltaic appliances is increasing in day-to-day applications. Many manufactures are producing solar panels and PV cells.

Why is a four-wire measurement important in a solar cell test?

The relationship between the two might need to be adjusted for the resistances of the wires, as in the example we described above, but overall the four-wire measurement is a way to accurately get current and voltage information of a device. A Kelvin or four-wire measurement is essential to getting accurate IV data while testing a solar cell.

Can liquid-cooled battery thermal management systems be used in future lithium-ion batteries?

Based on our comprehensive review, we have outlined the prospective applications of optimized liquid-cooled Battery Thermal Management Systems (BTMS) in future lithium-ion batteries. This encompasses advancements in cooling liquid selection, system design, and integration of novel materials and technologies.

What is a liquid cooled battery system?

Immersed liquid-cooled battery system that provides higher cooling efficiency and simplifies battery manufacturing compared to conventional liquid cooling methods. The system involves enclosing multiple battery cells in a sealed box and immersing them directly in a cooling medium.

Do lithium ion batteries need a cooling system?

To ensure the safety and service life of the lithium-ion battery system, it is necessary to develop a high-efficiency liquid cooling system that maintains the battery's temperature within an appropriate range. 2. Why do lithium-ion batteries fear low and high temperatures?

Are lithium-ion batteries temperature sensitive?

However, lithium-ion batteries are temperature-sensitive, and a battery thermal management system (BTMS) is an essential component of commercial lithium-ion battery energy storage systems. Liquid cooling, due to its high thermal conductivity, is widely used in battery thermal management systems.

Are lithium-ion batteries a new type of energy storage device?

Under this trend, lithium-ion batteries, as a new type of energy storage device, are attracting more and more attention and are widely used due to their many significant advantages.

What is an immersion cooling system for lithium ion batteries?

An immersion cooling system for lithium-ion battery packs that uses glycol-based coolant and a sealed case to cool the batteries uniformly and efficiently. The battery pack has cells held by cell holders inside a sealed case filled with coolant. The coolant surrounds the cells and circulates to extract heat.

What types of batteries are used in energy storage systems?

The most common type of battery used in energy storage systems is lithium-ion batteries. In fact, lithium-ion batteries make up 90% of the global grid battery storage market. A Lithium-ion battery is the type of battery that you are most likely to be familiar with. Lithium-ion batteries are used in cell phones and laptops.

How are batteries used for grid energy storage?

Batteries are increasingly being used for grid energy storage to balance supply and demand, integrate renewable energy sources, and enhance grid stability. Large-scale battery storage systems, such as Tesla's Powerpack and Powerwall, are being deployed in various regions to support grid operations and provide backup power during outages.

What is a battery storage power station?

A battery storage power station, also known as an energy storage power station, is a facility that stores electrical energy in batteries for later use. It plays a vital role in the modern power grid ESS by providing a variety of services such as grid stability, peak shaving, load shifting and backup power.

What is a battery storage system?

Large-scale battery storage systems, such as Tesla's Powerpack and Powerwall, are being deployed in various regions to support grid operations and provide backup power during outages. Batteries play a crucial role in integrating renewable energy sources like solar and wind into the grid.

Which battery is best for a 4 hour energy storage system?

According to the U.S. Department of Energy's 2019 Energy Storage Technology and Cost Characterization Report, for a 4-hour energy storage system, lithium-ion batteries are the best option when you consider cost, performance, calendar and cycle life, and technology maturity.

What is a battery storage power plant?

Battery storage power plants and uninterruptible power supplies (UPS) are comparable in technology and function. However, battery storage power plants are larger. For safety and security, the actual batteries are housed in their own structures, like warehouses or containers.

What type of batteries are used in electric vehicles?

There are four main types of batteries that are used in electric vehicles, namely ultracapacitors / supercapacitors, lead-acid batteries, nickel-metal hydride batteries and lithium-ion batteries. In the ultracapacitor polarized liquid is stored between an electrode and an electrocyte.

Which battery is best for electric cars?

Li-ion batteries are the preferred choice for modern electric cars due to their advanced rechargeable battery technology. However, they are relatively expensive to produce compared to other battery types. Nickel-Metal Hydride (NiMH) batteries gained commercial use in the late 1980s.

What are electric car batteries used for?

Beyond their 1500 charges and useful lifespan in a vehicle, electric vehicle batteries can be used for energy storage where performance isn't so important. For example, they can be used in motorhomes to store solar power, or as a backup for a power cut in our homes. Why are electric car batteries so expensive?

What is an electric vehicle battery?

An electric vehicle battery is a rechargeable battery used to power the electric motors of a battery electric vehicle (BEV) or hybrid electric vehicle (HEV). They are typically lithium-ion batteries that are designed for high power-to-weight ratio and energy density.

Which battery is best for an EV?

NiMH batteries are known for their recyclability and are proven to be a suitable option for EVs, with an average battery life of 5-7 years. Lead-Acid batteries, formulated in 1859, are the oldest type of battery still in use. They are known for their low cost but have a shorter lifespan of around 3 years.

What type of battery should I use?

Nowadays, Lithium-ion batteries are by far the most widely used, this is due to them recharging quickly, being robust against temperature changes, and being able to maintain power for long durations, with bursts of very high power.

Why do batteries need foam?

Foams also act as thermal and electrical conductors, depending on their material and the compression amount within the battery. An extra layer can be added to the foam to make it more suitable for EMI shielding. Battery components need protection from electromagnetic waves due to their high frequencies and small size.

Why do EV batteries use foam?

Regarding EV battery production, foam ensures optimal performance and longevity. Foam is widely used as an insulation material within battery packs, protecting the cells from extreme temperatures and vibrations. This insulation not only enhances safety but also helps maximise energy efficiency.

What materials are used to make EV batteries?

One plug-in hybrid EV built in China is already using a thermoplastic polypropylene compound instead of aluminium for its battery case cover, providing savings in weight. Other EVs now in production around world are using several thermoplastic materials for components such as cell carriers and housings, battery modules and battery enclosures.

What type of foam is used for EV batteries?

Polyurethane foam, silicone foam, and Ethylene-Vinyl Acetate (EVA) foam are commonly used foams in EV battery manufacturing. Each type serves specific purposes, such as thermal, electrical, and shock absorption. What are some advancements in foam technology for EV batteries?

What is the best insulation for a battery pack?

Additionally, polyurethane foam provides structural support, reducing the risk of damage due to shocks or vibrations. Silicone foam, another popular choice, excels in maintaining electrical insulation. Creating a barrier against moisture and dust ingress ensures the battery pack's long-term reliability.

Why should you use a dielectric battery foam?

These foams are built with fire-resistant materials, ensuring if something such as thermal runaway occurs in the battery, the foam will be an essential factor in reducing the chances of spreading. Dielectric foams and insulation are critical components to protecting the battery cells as they expand and contract while in use.

What materials are used in a battery?

Throughout the battery from a single cell to a complete pack there are many different materials. Aluminium, copper, nickel plating etc

What are battery packs?

Battery packs are constructed from two or more individual cells or batteries. There are two basic types of battery packs: primary and secondary or rechargeable. Primary batteries are disposable, non-rechargeable devices. They must be replaced once their energy supply is depleted.

What are the components in a battery pack?

Electronics and software are becoming standard components found in battery packs today. These components may consist of: Inside of custom battery pack showing electronics, components, and materials. Many of these components will be a part of the battery management system (BMS).

What is the best material for a battery pack?

If the batteries will be mounted into the device, such as on the handle or in a separate housing that will need to be accessible, injection molded plastic is commonly used. In some circumstances, metal casings will be required for the battery pack. This option is suitable for battery packs that will be used for traction applications.

What are the different types of battery packs?

There are a lot of different kinds of packs. The battery pack is composed by single cell through series or parallel. Parallel increase capacity, voltage constant. Series increase voltage, capacity constant. For example, 72V 45Ah can be assembled by 3.6V 2500mah cylindrical battery cell in the mode of 18 parallel and 20 series.

What are the components of a battery?

All batteries will have components such as anodes, cathodes, and electrolytes, yet these components will be made of specific materials based on whether a customer selects a lithium-based battery, alkaline battery, or nickel-based battery.

How does a flywheel energy storage system work?

Flywheel energy storage technology works with a large, vacuum structure-encased spinning cylinder. To charge, electricity is used to drive a motor to spin the flywheel, and to discharge the motor acts as a generator to convert the spinning motion's energy back into electricity.

What is the largest flywheel energy storage system in the world?

Image: Shenzen Energy Group. A project in China, claimed as the largest flywheel energy storage system in the world, has been connected to the grid. The first flywheel unit of the Dinglun Flywheel Energy Storage Power Station in Changzhi City, Shanxi Province, was connected by project owner Shenzen Energy Group recently.

Are flywheel energy storage systems feasible?

Vaal University of Technology, Vanderbijlpark, Sou th Africa. Abstract - This study gives a critical review of flywheel energy storage systems and their feasibility in various applications. Flywheel energy storage systems have gained increased popularity as a method of environmentally friendly energy storage.

Can flywheel energy storage improve wind power quality?

FESS has been integrated with various renewable energy power generation designs. Gabriel Cimuca et al. proposed the use of flywheel energy storage systems to improve the power quality of wind power generation. The control effects of direct torque control (DTC) and flux-oriented control (FOC) were compared.

What is flywheel/kinetic energy storage system (fess)?

and high power quality such as fast response and voltage stability, the flywheel/kinetic energy storage system (FESS) is gaining attention recently. There is noticeable progress in FESS, especially in utility, large-scale deployment for the electrical grid, and renewable energy applications. This paper gives a review of the recent

What is a 30 MW flywheel grid system?

A 30 MW flywheel grid system started operating in China in 2024. Flywheels may be used to store energy generated by wind turbines during off-peak periods or during high wind speeds. In 2010, Beacon Power began testing of their Smart Energy 25 (Gen 4) flywheel energy storage system at a wind farm in Tehachapi, California.

What is the voltage of a lead acid battery?

The 24V lead-acid battery state of charge voltage ranges from 25.46V (100% capacity) to 22.72V (0% capacity). 48V Lead-Acid Battery Voltage Chart (4th Chart). The 48V lead-acid battery state of charge voltage ranges from 50.92 (100% capacity) to 45.44V (0% capacity). Lead acid battery is comprised of lead oxide (PbO2) cathode and lead (Pb) anode.

What is a 6V lead acid battery?

Here we see that a 6V lead acid battery has an actual voltage of 6V at a charge between 40% and 50% (43%, to be exact). The voltage spans from 6.37V at 100% charge to 5.71V at 0% charge. It is also important to note that lead batteries have a depth of discharge (DoD) close to about 50%.

What is a 12 volt lead acid battery?

For example, a 12-volt lead acid battery has a nominal voltage of 12 volts. However, the actual voltage of a lead acid battery can vary depending on its state of charge, temperature, and other factors. The state of charge (SOC) of a lead acid battery refers to the amount of charge remaining in the battery.

What is a 48V lead acid battery?

The 48V lead-acid battery state of charge voltage ranges from 50.92 (100% capacity) to 45.44V (0% capacity). Lead acid battery is comprised of lead oxide (PbO2) cathode and lead (Pb) anode. The medium of exchange is sulphuric acid. Most common example of lead-acid batteries are car batteries.

What is the float voltage of a 12V lead acid battery?

Meanwhile, the float voltage of a sealed 12V lead acid battery is usually 13.6 volts ± 0.2 volts. The float voltage of a flooded 12V lead acid battery is usually 13.5 volts. It is important to choose a battery with a voltage range that is appropriate for the application in which it will be used to ensure optimal performance and longevity.

What is the state of charge of a lead acid battery?

The state of charge (SOC) of a lead acid battery refers to the amount of charge remaining in the battery. The SOC of a lead acid battery can be determined by measuring its voltage using a multimeter or other device. As the battery discharges, its voltage level decreases. Conversely, as the battery is charged, its voltage level increases.

What is a battery storage power station?

A battery storage power station, also known as an energy storage power station, is a facility that stores electrical energy in batteries for later use. It plays a vital role in the modern power grid ESS by providing a variety of services such as grid stability, peak shaving, load shifting and backup power.

What are the different types of energy storage?

The different types of energy storage can be grouped into five broad technology categories: Within these they can be broken down further in application scale to utility-scale or the bulk system, customer-sited and residential. In addition, with the electrification of transport, there is a further mobile application category. 1. Battery storage

What are the different types of electricity storage systems?

Electricity storage systems (ESSs) come in a variety of forms, such as mechanical, chemical, electrical, and electrochemical ones. In order to improve performance, increase life expectancy, and save costs, HESS is created by combining multiple ESS types. Different HESS combinations are available.

What are the most popular energy storage systems?

This paper presents a comprehensive review of the most popular energy storage systems including electrical energy storage systems, electrochemical energy storage systems, mechanical energy storage systems, thermal energy storage systems, and chemical energy storage systems.

What is a battery energy storage system?

Battery energy storage systems are generally designed to be able to output at their full rated power for several hours. Battery storage can be used for short-term peak power and ancillary services, such as providing operating reserve and frequency control to minimize the chance of power outages.

What are the different types of energy storage batteries?

ECESS are Lead acid, Nickel, Sodium –Sulfur, Lithium batteries and flow battery (FB) . ECESS are considered a major competitor in energy storage applications as they need very little maintenance, have high efficiency of 70–80 %, have the greatest electrical energy storage (10 Wh/kg to 13 kW/kg) and easy construction, .

What are electrochemical energy storage systems?

Electrochemical energy storage systems have the potential to make a major contribution to the implementation of sustainable energy. This chapter describes the basic principles of electrochemical energy storage and discusses three important types of system: rechargeable batteries, fuel cells and flow batteries.

What are the three types of electrochemical energy storage?

This chapter describes the basic principles of electrochemical energy storage and discusses three important types of system: rechargeable batteries, fuel cells and flow batteries. A rechargeable battery consists of one or more electrochemical cells in series.

What are the different types of energy storage methods?

Currently, common energy storage methods include pumped storage, mechanical storage, electrochemical storage, power-to-gas, and others. Fig. 1 (b) shows the distribution of these methods. Pumped storage remains the dominant global technology, accounting for 94 % of total energy storage.

What is the difference between mechanical and electrochemical energy storage?

Storing mechanical energy is employed for large-scale energy storage purposes, such as PHES and CAES, while electrochemical energy storage is utilized for applications that range from small-scale consumer electronics to large-scale grid energy storage.

What are electrochemical energy storage/conversion systems?

Electrochemical energy storage/conversion systems include batteries and ECs. Despite the difference in energy storage and conversion mechanisms of these systems, the common electrochemical feature is that the reactions occur at the phase boundary of the electrode/electrolyte interface near the two electrodes .

What technology is used for energy storage?

The last-presented technology used for energy storage is electrochemical energy storage, to which further part of this paper will be devoted. Electrochemical energy storage is one of the most popular solutions widely used in various industries, and the development of technologies related to it is very dynamic.

How do I test a solar cell?

You can effortlessly test the efficiency of your solar cell device using the Ossila Solar Cell Testing Kit — which combines our solar simulator with our source measure unit and test board. There are several methods used to characterize solar cells. The most common and essential measurement you can take is the current-voltage (I-V) sweep.

How often should a solar PV system be tested?

A solar photovoltaic (PV) system is required to be rigorously tested as part of the commissioning process and periodically throughout its subsequent lifespan. This is to test both the quality of the installation and the quality of its performance.

Can you test a solar cell using sunlight?

Of coruse, you could use actual sunlight, but this would introduce an uncontrollable variable. To test solar cells reliably, you need to maintain controlled conditions within your lab — and this is impossible to do while allowing direct, unfiltered sunlight onto your testing equipment.

Can solar cells be tested reliably?

To test solar cells reliably, you need to maintain controlled conditions within your lab — and this is impossible to do while allowing direct, unfiltered sunlight onto your testing equipment. Additionally, many potential solar cell materials are unable to withstand weathering effects during the early stages of development.

Why do solar panels need to be tested?

So continuously verifying system performance is essential. But the priority is safety, and because the panels are connected to the electricity grid and generate electricity themselves, maintaining the safety of the system is also essential and strictly regulated. What are the two types of solar PV testing?

Why is a four-wire measurement important in a solar cell test?

The relationship between the two might need to be adjusted for the resistances of the wires, as in the example we described above, but overall the four-wire measurement is a way to accurately get current and voltage information of a device. A Kelvin or four-wire measurement is essential to getting accurate IV data while testing a solar cell.

Do you have problems with your solar panels?

Nearly seven in 10 owners had had no problems with their solar panels in our survey of over 2,000 owners.* The most common – and most serious – problem owners face is with the inverter. In some cases inverter problems mean you don't get any usable renewable electricity. It can also be a pricey problem to fix.

What happens if you touch a solar panel?

If you touch the solar panels you will feel the heat. But usually it is not going to be a problem. A solar panel will not turn solar energy into direct current until there is a circuit. If there is no circuit, the solar panel will just “sit there” as the photons will not be converted into electricity.

What happens if a solar panel is not connected to a load?

This DC current is then converted by the solar inverter to alternating current (AC). The excess electricity can be stored or sent back to the grid through processes like net metering. So, what happens if a solar panel is not connected to a load or a battery? Well, the system remains in an open circuit condition.

What happens if a solar panel system is not installed properly?

If your solar panel system is not properly installed, it may cause problems in the future. For example, the system may not be operating correctly, meaning it won't produce as much energy as it should.

What happens if you leave solar panels unused?

When you plug them back into the system the charge should be where you left them off. Provided of course you did not leave the batteries for too long. Batteries will self discharge eventually, so do not leave them unused for prolonged periods. What Happens to Excess Solar Power Generated? Solar panels always produce energy when the sun is out.

How do I know if my solar panels are bad?

Check the wiring and connectors that join the solar panels, inverters, and electrical system. Faulty wiring often contributes to problems with solar panel connections. The most frequent issue is a poor connection between the wires and the terminals on the inverter or the solar panels. Corrosion or damage could be responsible for this.