Updating 2001 GEM Controller to Handle Chevy Volt Lithium Batteries

Last year I restored a 2001 GEM 4 and, in the process, I replaced the 6 lead batteries with two 72 volt Chevy Volt lithium batteries. The problem is the controller cannot be programmed make use of the batteries. The run limit is 65-72 volts whereas the battery range is 53-72 volts.

Does anyone know if the controller can be easily updated and what the hardware would be and the effort?

Many here made the same mistake.
The problem in not the car, but the batteries. 18s battery is not a 72v battery. It is a 66v battery.
Did you do this on your own or take the sellers word for it.
Worse case is they are from ********* in Ca.
He also claims to include bms, another lie.
Chevy Volt absolutely needs a FULL bms. Do you have a picture. We can help.

Thanks for replying so quickly.

Here is a picture of the front battery. There is a duplicate battery under the back seat. They are hooked up in parallel. You can see the BMS module on the front but it’s not actually being utilized in this installation.

I use a Victron Energy BMV-700 Battery Monitor to monitor the state of the batteries. Currently they are showing charged to 70.26 volts.

I have a Schauer battery charger in the car that will charge the battery to just under 72 volts.

And yes, I did all the work myself.

Yes, I can see you are another victim of ********.
Sorry, that you did not check here first.

I don’t see any balance leads going to a BMS other than the fake one shown.

Even if you get car to run on 66 volts performance will not me good. We go the other direction. Using up to 24s 88 volts nominal.
Can you show how your bms is connected to the two battery modules?

How long have you been running on this present rig?
Or is this a recent purchase/addition?

Get you money back. This guy is a crook…

I’ve had this running for a little over a year. Way past getting any money back.

The BMS modules are not actually hooked up. If I remember correctly when I installed the Schauer charger I was told the charger would be handling the management.

Not if it’s not connected to all the balance leads.

This guy bought one of Cruisin’s battery packs

That is only part of the problem. The charger is only handling the charge as a group, but it has no idea what is going on at the cellular level. When you start to go out of balance at the cell level things cascade out of control quickly. Running two packs in parallel multiplies the problem even more.

Old LAcid tech just overcharges all the batteries and any excess energy will turn to heat. Lithium is not tolerant of that at all. Heat is bad.

The other problem is that as sold, you are operating these batteries outside of their comfortable design specs. Running a 66v pack up to 72v is actually hard on them.

It is difficult to tell in your first pic(I see a few gaps), but are there any signs of pack separation in your other battery?

@pauldivaniii when a lead acid battery system is said to be a 72V system there is a bit more to understand. The batteries installed are called 12V batteries but their fully charged voltage is typically 12.7V and by the time you discharge them to 12V(don’t do this) they are depleted and possibly damaged. So a 72V system really operates at about 76.2V and when just off the charger those batteries are at 13.8V each so 82.8V.

If someone gives your a 72V battery pack which is “fully charged” at 72V you have the wrong guy…

FYI, cells of a 12V lead acid battery are said to be 2.0V cells so there are 6 cells in a 12V battery.
Lithium Ion batteries are rated at 3.7V per cell with peak charged voltage of 4.2V but you usually don’t want to charge to 100% so 4.1V is a better top voltage.
Lithium Phosphor are 3.3V normally… IIRC 3.6V is fully charged.

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State of charge in a typical Lead Acid 12v battery

12v battery SOC%

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Money back, from Allan? Isn’t all of of his crap sold with a “taillight warranty”?

Well, look on the bright side, you got ripped off, but at least it hasn’t burned your house down yet.

Now we know what this owner is dealing with and has, what are the options going forward?
Testing each cell and seeing what shape they are all in and if good, building some extender modules which take each pack upto the proper voltage and then get the charger and BMS configured?


You mean adding on a few extra cells?
I didn’t think these were easy to split/Extend.

I really appreciate everyone’s input. This is really great, so, thank you.

So, I did some additional research and analysis based on the above and the max voltage (4.2) and min voltage (3.0). The batteries I have are a package of a 36 cell (12 in series/3 parallel) with an 18 cell (6 in series/3 parallel). This would give a max charge (at 4.2 volts) of 75.6 volts, a minimum recommended charge (at 3.0 volts) of 54 volts and 80% at 71.28 volts. The cart runs fine from the 72 volts that I can charge it to down to the 65 volts that the GEM controller will allow it to run to)

The controller for the 2001 GEM cannot be reconfigured to support a minimum voltage below 65 volts because that’s the lower limit for the normal lead acid batteries.

So, from my perspective there are two issues:

1: Do I need to get a BMS for each battery and run the charging through them? Will the BMS that is on each battery, which I am not charging through at the moment, usable and I should split the charger output and run a wire to each battery’s BMS?

2: I really need a more contemporary controller that can be programmed to support lithium batteries. Does anyone have experience in installing a more contemporary (I think 2006 GEM or later) controller in a 2001 and would that potentially require me to completely change out the wiring harness and 12V DC controller board? If I am pretty sure that if I can extend the usable range of the batteries from 71.6 or so down to 54 volts I can double or triple the range of the vehicle.

This has all been done. Don’t reinvent the wheel.
The problem is your battery/bms system. Do you want to make do or start over?

To use what you have. Connect the two 44v modules in series for 88 volts. Discard the two 22v 6s modules or buy two more to parallel with first set. (Get it working first)
Then get a 24s bms good for at least 300 amp peak. I like ant or jk bms. Cheap and work well.


Do not charge those cells to 4.2v. Chevy wont let you take them over 4.07v. 4.2v will eventually be a big problem.

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Read carefully what Inwo and LithiumGods just said. ^^^

Many here have already gone this route. Inwo just gave you a plan to fix what you have, and if not enough range we can expand on that later.

If you thought it worked well at 72-65 you are going to be amazed how well it works at 88v. Basically, when the packs are dead and need a charge, you are still running around like your pack now “Fresh” off the charger.

One thing you still seem to be missing is that you do not have 4.2v cells! Sure, they can be pushed up that high but it is not good for them. It REALLY stresses them out! Even the factory saw this error and has dialed them back. It is amazing that you have run a year on them and it might be because you haven’t been running them at 4.2 for very long. (did I misread that?)

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Maybe it’s me but I wouldn’t take my lithiums down to 3.0V since that is the BOTTOM just like I don’t take them up to 4.2V since it is the TOP and at both ends not-good things start to happen. Since there’s not a lot of charge capacity above 4.1V I take mine to 4.1V every now and then but mostly 4.0 and I never go below 3.3V. Besides, there’s not much below 3.4 or 3.5 so generally If I have what shows 70-75% I will take it out for a few miles and on return the SOC is showing 60-65% which is in the 3.4-3.3V range. That’s me.