How to Wire an Li-BIM Lithium Battery Isolator

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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.

40 thoughts on “How to Wire an Li-BIM Lithium Battery Isolator”

  1. Hello,

    I am installing a 600W SOLAR | 400AH LifeP04 BATTERIES inspired on your first and only available diagram, the new specific diagram, is almost the same as what I planned, juste a few differences. But I am trying to read alld your guide to make sure I do the thing right.

    Thank you for all the stuff you publish


    1. Hi Nate,

      Thanks for the great stuff! I am converting a 2008 Dodge Sprinter. Where did you mount your LI-BIM 225 and how did you run wire to the vehicle battery?

      Much appreciated!


  2. hi Nate, I messaged you last month and wanted to say thanks for the reply….. in looking into this a bit more I settled on using your 350/400 setup… the only thing is, I will be using agm batteries as I have 7 of them available to me ..(I got really lucky) . my question is what do I need to change aside from the type of isolator you have on that diagram and will the Victron inverter charger work with agm…thanks in advance

    1. Thank you for all your wiring diagrams. You have made it easy for the rest of us. Why do you say to add a 300 app fuse at each terminal. I’ve seen other places including battle born that say you do not need a fuse. Can you explain please? Thank you!

      1. You need a fuse protecting the wire from each non-regulated source of power. If any of those wires short to ground, there is a potential for 1000+ amps from the battery through the wire to flow through it to the short, causing a fire. A fuse will disconnect that power.

  3. Thank you for all the great work!

    Amazing. I was up until 5am PST today wiring up a simpler set up of just battery isolator and auxiliary battery sans solar componets and an hour and a half later, your email comes in about how to wire the isolator. How did you know?! I was looking for a wiring diagram, but just dissected one of the solar ones. It would be great if you could strip down the solar part one of the wiring diagrams and post it (maybe you already did?) For those who are building out without solar (for the time being).

    Thanks Nate!

    1. Awesome! Glad it came at the right time! Re: Charging without solar… Hopefully, I’ve made it fairly straightforward for you to see how to omit/delete the solar charging leg of my wiring diagrams as I don’t have a wiring diagram that does not include solar charging available, but if you need me to make one for you; I can do that under my custom wiring diagram service:

  4. A bit confused on wire/fuse sizing which is normal for me. I just got the LI-BIM 225. The larger posts on the BIM go to the positive house and start batteries but then the ground is a much smaller connection which to me indicates a major difference in amperage usage and wire size needed. I can’t see how this smaller terminal can carry the amps needed for when/if I need to use the sig. circuit to jump start the engine from the house batteries. I would think that the battery to battery connection would need at least the wire size of a normal battery cable and this would be for both positive and negative. Even your parts list shows two different wiring sizes. The instructions that came with tell me nothing but how the BIM works but does show the grd. terminal connected to both batteries and to vehicle grd. Is there an assumption that my house batteries are grounded to the van itself, which it is not.

  5. Thank you for the reply, but now have fa few more questions.
    First, where did your 70% alt output come from? My 2018 Transit has an alternator rating of 150A and I’ve been told but haven’t been able to verify it that the vehicle itself will use an average of 70A just to run itself, considering the amount of electronics on new vehicles I could this to be true.
    Second, since the BIM will allow self jump starting wouldn’t it be more feasible to use starter draw amperage since that would be most likely be a larger draw even if at a shorter time frame?
    Third, If I use your calculator of 20′ wire at 105A (70% of 150) it tells me to use 1/0 wire and 150A fuses. This seems a bit extreme since the house battery to starter cable looks closer to maybe a 2AWG and the alternator wiring is maybe half that size. Since the battery is under the seat the length of those wires I would think would be close to the same distance as my house batteries are.
    Fourth, Ford does not want any extra wiring attached to the positive battery post so they provide what they call the Customer Connection Point. This is a 60A fused connection located at the pre-fuse box under the seat. It also has only about a #10 size terminal which I think would be way to small for a 1/0 wire not to mention a 150A fuse so any ideas how to make this BIM work?

    1. 70% is typically the absolute MOST an alternator can produce after taking care of vital engine charging systems.

      Re: Self jumping. Not really… Think about the gauge of most jumper cables. Most are 6gauge wire. Most wires going from House to starting battery through the Li-BIM will typically be at least 2 AWG.

      You’re getting a 1/0 result based on voltage drop due to the length; not max amperage.

  6. Hello Nate,

    First off, I would just like to thank you for all of the hard work you’ve done creating documents around van builds. I have personally bought the Explorist.Life package from Battle Born and have pretty good success with it so far.

    One part where I am running into trouble is with the Lithium Isolator that came with the kit. My Ford Transit’s alternator puts out a voltage of 14.7-14.75V, which is too high for the isolator to kick on. I reached out to Battle Born Batteries, and they were very helpful and mentioned another device I could add before the isolator, but it is very expensive. Would you happen to have any ideas on how I could get the isolator to switch on or should I go ahead and buy a different isolator?

    Thanks for the help in advance! =]

    1. Darn! What a silly problem to have…but a problem nontheless… So, what I’d probably be doing in that case, is running a battery to battery charger instead of an isolator. Victron makes something called a ‘Buck Boost’ that will help with that and they’ve recently come out with a 12v to 12v charger for that as well.

  7. Hey Nate,

    What gauge wire do I need to use to connect the house battery negative to the chassis? The positive wires need to be thick for the AMP draw from the alternator, but do I need something so thick for the negative to chassis connection?

    I’m not understanding WHY the ground is needed in this situation to the chassis or starter battery, but it wouldn’t work back to the house battery.

    Thanks so much

  8. I love this blog post! Thank you so much for putting all of these articles together! One question, where do you get your momentary switch from? All the rocker switches I have ordered are too large for the holes in the dash of my sprinter. They seem to be smaller than the norm… Do you know what these are specifically called? TIA!

  9. Hello Nate, your website is super helpful thank you for posting all this wonderful info. I have question regarding wire length and voltage drop. I have a roughly 45ft run from my truck to the middle of my Airstream trailer where I will be installing 3 Battle born lithium batteries 100ah each. The calculator recommends 4/0 gauge but that is not cost effective. If i raise the voltage drop to 5% i can use 1/0. Will that difference be negligible in the charging? Thanks in advance for your help!


  10. Hey Nate,

    This is awesome! I’ve got it all set up as you’ve shown (without the momentary switch though) and I noticed that the Li-Bim seems to not be turning off (even with the ignition turned off). I noticed this because I turned off the switch on the busbar (the big red one you recommended on your other excellent busbar post) and this doesn’t turn off lights I have wired to that part of the busbar. Before I wired the isolator, these lights would turn off. My question is: is this expected behavior? Should I assume this is scenario 2 above? Thanks!!!

  11. When I upgraded my coach batteries to 600 amp hour AGMs, it took months to get it all working some what correctly. That was 9 years ago and the batteries are shot. I am thinking about upgrading to Lithium and I am trying to not make the same mistake of believing everything I read about batteries and charging. Among the conflicting information I am getting is that the LI-BMI will connect the two batteries only when the alternator is producing, or as you article suggests also when the LI-BMI senses certain voltages . The latter worries me as I do not think the LI-BMI is programmed to consider my case. I have both a solar charger and a AC to DC charger on BOTH my house and coach batteries. It took quite a bit of work to set every thing up so that one device does not cause the other to think that a battery is fuller than it is. I do not want the LI-BIM to complecate that issue. So does it connect the two batteries ONLY when the alternator is producing and certain other conditions exist?

  12. Allan Galbraith

    Hi Nate:
    I have a kudo and a question:
    First, I enjoy all of your videos and am heavily relying on them in my Promaster conversion.
    Second, regarding the wiring of the Li-BIM, my understanding is that the wiring (2/0) from the LI-BIM BATT CHASSIS STUD to the Starting Battery is downstream from the Alternator-Starting Battery. My way of thinking, after reviewing your first 2 scenarios is that the Alternator is always sending a charge to the Starting Battery and the Li-BIM simply opens or closes the transmission of a charge from the Starting Battery to the House Batteries, depending on the comparative balances you described in the 2 scenarios.
    Please advise if I understand this wiring.
    Now, to figure out the optimal placement of the Li-BIM!

  13. Hi.
    I’m very much an electrical novice and could use some advice.
    I upgraded my two AGM batteries to two Battle Born LiFeP04 100Ah batteries and I’m noticing that the batteries don’t seem to be charging fully, and once they get below a certain level they quit charging all together (requiring me to briefly bypass the ACR to start charging again). Do I need to replace these with an isolator and lithium-specific charge controller or is there something I can do that doesn’t require me to purchase all new components? I’ve been running this system for about 18 months (living out of the van full time) and currently have some time and access to a workspace for upgrades/repairs.

    I’m using the following components that are made specifically for Lead Acid batteries:
    Genasun GV-10 Lead-Acid MPPT Solar Charge Controller
    Blue Sea SI-ACR Automatic Charging Relay 7610


    1. Yeah, neither of those products are really set up for lithium batteries.

      The MPPT may not be able to deliver a high enough voltage to fully charge lithium batteries.

      The Isolator may not charge the Lithium batteries because the resting voltage of lithium batteries is higher than the ‘connect’ setpoint of the isolator, so the isolator doesn’t thing the battery is low, and therefore won’t charge.

  14. Hi,
    I am planning on using a DC to DC charger instead of a relay. Are there any special considerations for doing this?

    I am choosing this route for a couple reasons:

    1. I don’t have LiFePo4 batteries.
    2. I didn’t want to buy that much 2/0 wire showed in your wiring diagrams.
    3. The charger can “amp up” the current it is pulling to compensate for voltage drop.
    4. A charger can compensate for the different charging phases.

    What I’m wondering is if having solar power from the MPPT and power from the alternator will have an interaction I need to account for.


    Also, do you have a patreon account? Your wiring diagrams have cut months off my work and I didn’t actually buy my batteries using your Amazon affiliate links, but I want to say thank you in a meaningful way.

    1. I agree with the use of DC to DC chargers and have started incorporating them into my newest systems:

      I don’t have a patreon account as I don’t have anything additional to offer that I’m not just making 100% public/free. I appreciate that though. The best ‘thank you’ you could give is to simply share my videos/blog posts when you see somebody seeking information. 🙂

  15. Nate, been following for awhile now. I’m new to RVing retired and looking forward to boon docking the country. I have a 2019 Thor Chateau 24F, I’m upgrading the (1) acid battery house to (2) lithium ions. I need to upgrade the factory installed BIM to the BIM 225. The RV already has a factory installed Momentary switch to use the house batteries as a jump unit. I want to be sure I understand the wiring, can I take the wires off the factory install BIM and install them on the appropriate studs of the BIM 225. If I understand your wire diagram the factory wiring should work. Thanks for your time.


    1. I’m not sure how your current isolator is wired but if those wires meet the given parameters outlined in this blog post, yes, they could be a direct switch. If they did not meet the parameters set in this blog post, no, they could not be a direct switch. You’ll have to check all of that with a multimeter to find out which wires are delivering voltage at what time.

  16. Hi Nate, I’m so glad to have found your great DIY site… Thank you!
    I’m currently doing a build of a 2019 Ford Transit van and I’m installing the Li-225. The starter battery is under the driver seat and the fuse block is under the hood. The fuse block not being readily available has me thinking about just using a switch that the driver can engage to supply the 12v to the IGN stud. Do you see any problem with doing this?
    Currently, I have a 2/0 cable connected from the Li-BIM Coach stud to my coach battery, and both the IGN and SIG studs are unattached. I was surprised to see that there was 12v on my coach cable because I would have thought no voltage would be available without an ignition signal. Is this normal?
    Thanks for your help and great site!

    1. The main problem I can see with using a switch as you mentioned is that if you forgot to turn it off but turn the engine off, the isolator may still think the engine is on and will keep the batteries combined, potentially draining the start battery as you use your house battery bank.

      If the 2/0 wire is connected to the house battery bank and the ‘coach’ stud of the Li-BIM, you are seeing voltage at the ‘coach stud’ from your house battery bank. This is expected.

    2. Thanks Nate you’re definitely better then tech support… which I’m still waiting on a return call.
      I still scratching my head on the 2/0 cable that is attached to the Coach stud because the other end wasn’t attached to anything when I measured the 12v.
      Thanks again for your help!

      1. I’m not sure how the inner workings of the Li-BIM work, but there could be a tiny bit of voltage passing through or stored inside of the relay. I wouldn’t worry too much about that.

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