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How to Wire an Li-BIM Lithium Battery Isolator

How to Wire an Li-BIM Lithium Battery Isolator

The Li-BIM is a Battery Isolator specifically designed to work with Lithium house batteries. Lithium batteries like Battle Born batteries have a slightly higher resting voltage than their AGM or Lead Acid counterparts. The standard AGM tuned isolator will see this higher voltage as a ‘charging’ voltage and will not disconnect the starting and house batteries which means the starting battery is at risk for getting low when electronics are used from the house battery bank when the engine is off.

Also, the Li-BIM is unique because as the alternator is engaged, the Li-BIM will connect for 15 minutes; and disconnect for 20 minutes. It will repeat this cycle as long as you are driving. It does this because lithium batteries can draw a SIGNIFICANT amount of power at one time due to its low internal resistance. This is great for rapid charging, but this high-amperage draw can potentially overheat an alternator. This on/off cycling allows the alternator to cool down for 20 minutes between 15-minute charging bouts.

Recommended Parts for Wiring an Li-BIM Lithium Battery Isolator

Li-BIM Lithium Battery Isolator Wiring Diagram

This image is a wiring diagram for the Li-BIM Lithium Battery Isolator

How to Wire a Li-BIM Lithium Battery Isolator

There are 5 studs on the Li-BIM, You’ll need to attach a wire to each of them; and here’s where they need to go.

Wiring the Li-BIM Ign Stud

Ign:  This stands for ‘Ignition’ and needs to tap into a circuit that has 12v power when your vehicle is on.

One way to determine where to attach this is to use your multimeter;set to DC volts, OR a test light and connect the negative probe to the the metal of your vehicle.  Next, start pulling fuses, one-by-one in your fuse block and test each circuit with the key off; AND the key on. You’re looking for a circuit that shows 12v power only when the key is on.

Once You’ve found the circuit you’re going to use, use an Add-A-Circuit Fuse tap, insert a 5A fuse, and run a 18ga or larger wire from the Add-A-Circuit Fuse tap to a ¼” ring terminal and attach that to the IGN stud on the Li-BIM 225.

Wiring the Li-BIM Gnd Stud

Gnd:  This stands for ‘Ground’ and simply goes the a ground point on the metal chassis of your vehicle.  This can be on the body near the Li-BIM or it can be run all the way back to a negative busbar. This is up to you.

Wiring the Li-BIM Sig Stud

Sig:  This stands for ‘Signal’ and is simply a ground wire with a momentary switch wired in line.  You will want to mount the momentary switch near your steering wheel so you can reach it while trying to start your vehicle.

The point of this switch is so that you can force-combine your house battery bank and your starting battery in the case of your starting battery getting low.  Basically, when you push this switch; it gives you the ability to self-jump yourself without relying on another vehicle and a set of jumper cables.
This needs to be a 18ga or larger wire and will connect to the Sig stud of your Li-BIM with a ¼” ring terminal on one end and to the metal of your vehicle with a ring terminal on the other end.  On this wire, you’ll need to install a momentary push-button switch attached with two spade connectors.

Wiring the Li-BIM Batt Chassis & Batt Coach Studs

From these studs, you’ll run a wire to both your house battery bank (Batt Coach) and your Starting Battery (Batt Chassis).  You’ll need a 5/16” lug to connect these wires to the Li-BIM. On the ‘battery’ side of each of these wires, you will need to protect this wire with a terminal fuse of appropriate size.

Batt Chassis & Batt Coach Wire Size.

To determine the gauge of wire and the amperage of fuse you will need on each of these wires, you’ll need the following two pieces of information.

  • Alternator Size (Amps)
  • Distance from Starting battery to House Battery Bank

Take the amperage rating of your Alternator and multiply that by 0.7 (as 70% is the most amps your alternator can feasibly produce)

Plug the resulting amperage and the distance between your start and house batteries into this calculator and set the allowable voltage drop to 3%.

This is the wire and fuse size you will need to use.  There needs to be a fuse at each battery. Terminal fuses are my preferred type of fuse as they take up less space and require less hardware.

Li-BIM Parameters

Here is a list of conditions at which the Li-BIM will activate and deactivate:

The LI-BIM 225 senses voltages of the Chassis (Engine) and Coach (Auxillary) batteries. There are three senarios to when the connection will be made, each with their own response:

  • Senario 1: Engine is “on” with a Chassis battery voltage greater than 13.4V and a Coach battery voltage less than 13.3V
    • Response: The LI-BIM 225 will connect the batteries for 15 minutes, then disconnect the batteries for a wait time of 20 minutes. After this wait time, a new voltage reading will be taken of each battery. If the voltages remain within the scenario’s parameters, the response repeats.
  • Senario 2: The Chassis battery voltage is below 12.5V and a Coach battery voltage greater than 13.5V
    • Response: The LI-BIM 225 will connect the batteries for 1 hour, then disconnect the batteries for a wait time of 2 minutes. After this wait time, a new voltage reading will be taken of each battery. If the voltages remain within the scenario’s parameters, the response repeats.
  • Senario 3: The Normally Open Momentary Switch is pressed
    • Response: The LI-BIM 225 will connect the batteries for as long as the switch is pressed.

Daniel Harris

Thursday 21st of October 2021

Hi Nate, I have an LiBM 225 wired up the way you show in your wiring diagram, at first it seemed to be working as it should and was charging from the alternator. Then I wanted to test the momentary switch to see if it was working. When I did that I heard the noise from the LiBM connect, then disconnect when I released the switch. Now the LiBM seems to only charge if I am holding the switch and when I let go it stays disconnected and won't charge. I am not sure if the momentary switch I got is actually an NC instead of a NO or if there is something faulty in the LiBM? Any help in diagnosing this would be appreciated. While I would love to upgrade to a B2B charger, I don't know that I have the space to mount it without it being to close to the inverter and I worry about things getting to hot, so I might be stuck with having to get this to work.


Tom Burke

Thursday 19th of August 2021

Hi Nate, I installed the isolator, and for a few months it worked great. Now, I hear it click on, but I’m not seeing any added amps to my charge when it does. I changed the fuse on my Lynx Distributor, and still nothing. Do they LiBim isolators go bad? Any suggestions? Tom

Jay M

Friday 14th of May 2021

In a small 30A Class A motorhome (2015 Fleetwood Storm) how does the LI-BIM impact the items like the stairs - that are powered by the chassis battery when the ignition is on and the house batteries when the AUX switch is enabled.

I'm trying if it just goes in the exact place the current BIM is located and if it will have any negative impacts to those systems.

I'm also guessing once I have connected the new lithium batteries and solar the AUX switch (that disables the house batteries) will not be functional.

Nate Yarbrough

Sunday 16th of May 2021

Everything on the 'house' side should remain unchanged and be unaffected when using the Li-BIM.


Friday 7th of May 2021

Thank you!

Jay Dooley

Monday 25th of January 2021

Looking to protect my alternator. Do not want it to fry due to overload. Current system is 2-6v agm deep cycle. 100/50 victron charge controller. 2- 600w 24v renogy solar panels a regular BIM-225. Jayco has a 1200w inverter installed but will upgrade later I have 2 - 100ah BB lithium which I have not installed yet. Plan on 6 minimum and 2 Victron 12v multi's in the future to allow all 120 outlets and appliances to be active. With 10- 20 batteries total in 2 years.

Will the LiBIM 225 allow me to install the lithium batteries without damage to chassis alternator? Or am I still missing something?

Nate Yarbrough

Tuesday 26th of January 2021

The harder the alternator is worked, the higher the chance of overheating. There is no magic answer for determining when/where/how long your alternator will last when it is subjected to increased loads. I will say though, I generally, at this point, recommend DC DC chargers over Isolators. More info: