When you are looking to interconnect your lithium-ion batteries with your lead acid batteries, the only method we recommend is with a battery isolator or DC to DC charger in line between the two.
Do you need a battery isolator?
A battery isolator is the answer you're seeking. Battery isolators allow you to control the current flow in your off-grid electrical system. Some allow you to shut off any power drain with the flip of a switch. Some prevent your batteries from draining off each other. Regardless, a battery isolator will almost always improve a multi-battery system.
How do I connect a lithium ion battery to a lead acid battery?
When you are looking to interconnect your lithium-ion batteries with your lead acid batteries, the only method we recommend is with a battery isolator or DC to DC charger in line between the two. The most common application of this set up is for alternator charging.
Both lithium batteries and lead-acid batteries are rechargeable energy storage batteries, but they have very different characteristics. Without proper components in line to separate the two, the batteries cannot be used in conjunction. Please note that these components must meet the technical requirements, including protective measures.
Why do I need a lithium battery isolating unit?
You need this unit in line because lithium sits at a higher voltage and requires different charging parameters than lead acid. An isolating unit will disconnect the line between the batteries so that your lithium batteries do not continuously feed power into your starting battery.
What is a battery isolator?
A more complex version of a battery isolator also includes charge control. These are called DC to DC chargers and are frequently connected between two batteries. These DC-DC units allow very specific control of the current flowing between batteries and can help to properly charge a second battery.
When should you use a diode battery isolator?
Finally, a diode battery isolator is useful when you have multiple lead-acid batteries and want to prevent them from draining one another. Generally speaking, diodes only allow electrical current to flow in one direction.