Gem battery issues

My gem car has deka dominator 8g31 gel batteries in it. The date code is L16. I don’t use the car much this time of year and I noticed that when it’s sits my batteries drain down quite a bit. I can’t find anything that is drawing any current. I just tested it after a full charge and I get between 12.7 and 12.8 volts on all of them except one is 12.5 volts. I suspect I have a bad cell. I hooked it up directly to an automotive charger and it goes into defective on the charger. What will happen if i just use it like this? If I need to replace that one battery can I replace just the one with new? All the others test good.

I’m not sure if this is related but I did Keep it outside for 6 months with a cover on. I noticed that sometimes when I put it into forward gear it wouldn’t go I would have to cycle to switch back and forth or turn the main power on and off before it would work again. I’m wondering if moisture got into something. All the battery connections look nice and clean though.

If you aren’t going to use it, best to turn off all power (switch below seat) or charge it by unplugging/plugging back in every couple of weeks, minimum.
What you definitely DON’T want to do is replace just one battery, since the pack needs to be balanced, and you’ll throw of pack balance with one new/five old batteries.
It might be time to consider going lithium. That’s what I would do if I were in your situation.

As Andie’s Mom just said, the BEST thing to do is replace them all… BUT, if the other’s test well as you said, your batteries are suffering (you also) because of the ONE obviously bad cell in that bad battery. You NEED to replace just that one at least.

Harbor Freight sells a battery Load Tester for ~$20 bucks or have it tested free at most auto parts stores. I found the tester to be an invaluable tool to have.

Lastly, in doing the math, a battery with a bad cell will many times drop to ZERO. Average that in with the other s and you’ll find you probably have ~10 volts to the controller, etc. Lower voltage, higher amperage draw… You are not doing anything any good by keeping it.

Lastly (again)… I purchased a set of 6 - 12 volt batteries for my TH!NK at Napa using their sealed gel deep cycle Marine batteries. I u/s that DEKA’s are the best though, but I learned that afterwards. Mine ran ~$950 bucks and I use the TH!NK almost daily for short jaunts. I don’t have a long term result to tell ya, but these fit my $$$ needs at the time.


it’s true that the BEST option is to replace all the batteries in the pack at the same time with 6 identical batteries. The idea is that the electrical characteristics of all six should be very close, close enough that minor variations in internal resistance will not materially affect the voltage distribution across the cells during charge and discharge, Lead acid battery technology is not as sensitive to cell imbalance as some of the more modern technologies - say lithium. Some Lithium packs absolutely require a cell level battery management system to prevent damage to individual cells. I would not be too concerned with replacing one battery out of six, provided you use the same make, type and rating as the other five. The self discharge characteristics of lead acid will likely prevent long term imbalance problems. The caveat - unless the failure of the one cell you are seeing now was the result of a manufacturing anomaly - the other cells are likely to start failing one by one. Lead acid technology cell life is almost an exact science assuming routine use. Sporadic use (charge/discharge) can result in wildly unpredictable cell life. (Ever notice your 36 month battery fails after 37 or 38 months - its not an accident!!) :slight_smile:

Putting one of these in my new Gem to make up for a design problem. Polaris will add a battery, but no dealer near me.
Unfortunately I have not found a 6 battery balancer with display. This one does 5.
< $150
Two of them will do 9 batteries connected to cross balance. Solution for the 9x8v Gems.


Dave, what is the design flaw you are trying to fix??

Polaris tapped into the main battery for 12v power to the electronics. It unbalances the pack.
Factory update adds a 12v battery.

Duh … ! Unbelievable. Think I would have gone with a 48 to 12 converter, rather than adding significant weight - and finite battery life issues. - Different strokes …!

Duh is right. I think they do have dc to dc. If they do then I don’t know the issue.
It might be that electronics are so sensitive that a fail safe system is needed.
Hate to think that disconnecting the battery will brick the car. But who knows.

I think I might be ok. I pulled the dash because the gem wouldnt do anything except beep when I put it in forward or reverse. I found a wire was off of some relay or whatever it was. It still wouldnt go into gear until i cycled it on and off numerous times and then the large solenoid finally started clicking. It must have been a bit corroded or something.

I put it all back together and fully charged it and took it out for a few miles. It did drop down to about 88% with all the lights on, stereo and 4 speakers with lights in them. I put it back on the charger and after sitting a few days I have 2 batteries at 12.68 and the rest are between 12.8 and 12.9.

The only issue I’m still having is my brake lights stick on unless I slam on the brake pedal. I guess I’ll have to pull that apart.

When I do have to replace the batteries it sure would be nice if somebody had a plug and play lithium upgrade for these things.

Sounds like you are making progress with it. My GEM had been sitting for a while so I went thru all connectors and applied “Deoxit D100L” corrosion cleaner to each. Slip on spade lugs are the worst to corrode and/or lose tension to create intermittent connections. Multi pin connectors should be cleaned and lubricated as well. Disconnect - reconnect them several times - most are somewhat self cleaning if exercised. I usually perform this ritual on tractors and boats at least once a year to prevent problems.

I intend to upgrade to lithium batteries soon - but currently anything that approaches plug and play is very pricey !

they add 12V Battery 12AH 210CCA

Yes the Newer gems have a Sevcon 48v dc/dc converter. They tapped into the first 12v of the battery pack to ensure the vehicle would still run if the dc/dc converter fails. The unintended consequence is that the bmc is performing tasks during off time that could drain the constant 12v supply. As well there is no disconnect switch since the vehicle goes into hibernate mode if left off long enough.

Essentially the newer gems are a Polaris Ranger EV with the “Gem inspired” appearance and drive-line.

Can you post the battery instructions in case I decide to do it?
Can you get paid if I diy it? Or do you get in trouble?

The aux battery connects to the bmc but you need to reflash the bmc afterwards. Also for the machine to charge the battery when running/charging you need a relay added to your fuse panel.

Definitely cannot unless brought to a dealership plus you need their software to reflash.

Im back to be annoyed by this thing. I can fully charge it to 100% and with the main switch off im somehow losing battery power. It was reading 100%, I backed it out of my garage and it dropped to 70%. I plugged it in for maybe 30 seconds and unplugged it and it read 100% again. Its also way down on power, it used to spin the tires from a dead stop and run in the low 30s. Now its a dog and tops at 25. I cant believe my 2 year old batteries lost this much power.