LiFePo4 "7th battery" on a lead bottom GEM

So, 18 months later, my cauck (CArt-trUCK for the newbies) is still running. Put a bit less than 4k miles on it since the install of the lifepo4 booster pack. The pack has been rock solid. I can’t say that I’ve noticed any other problems or issues related to it.

Ended up reprogramming the controller to turn down the max speeds a bit more. Turf goes to 21 and road goes to 35. I think I also set the field weakening back to stock as I became less interested in coming up fast and would rather have my cauck go the distance.

Oh, yeah, actually there is one thing going wrong related to the pack, not really unexpected though. The charger fan is going out, should be an easy fix. I should probably fix that before it fails and adversely affect the performance of my cauck.

Dave, is there anything special I need to know about opening the little Chargery bricks or they pretty standard construction?


No, easy enough. Fan is temp controlled, may be ok.

I forgot about that… So, a few months ago, it was stopped while charging, I know it shuts off after it’s done, but will it shut off while charging if ambient is that cold? I’m in California, really cold nights (relatively speaking) where I live aren’t that common, it could have been one of those nights. I haven’t observed it doing that since I took an air nozzle to it. It’s a little noisy, but not too bad.

Fan only turns on when hot.

I know this is an old thread but I want to do this this lifepo4 booster hack my self. I have one laying around. I have a stock 02. Im pretty sure I need one of the super magical magnets. Not really sure where to get one. My big question I cant seem to find anywhere though…

Is there a way to make the 7th battery more of like a nitrous pack where I can kinda just flip a switch when I want to add more juice to motor? I have a 200a remote battery on off switch that connects to the negative terminal and was wondering if this was at all possible.

Yes, you can use a two position golf cart contactor. It might not last long switching under load.
Pm me or search for PayPal link to Magic Magnet. $135

no real advantage to making it on demand. Gem works great with the 7th battery and it increases range. I would leave it inline full time.


It sounds like he just wants a Button to hit.


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I stand corrected. No good can come from switching on the fly.

BUT, try switching a shunt across field. That is done all the time in industrial applications.
We just need someone silly enough to do it.
Measure field resistance. ~2ohms wag.
Start with 20%. Another wag. .4 ohms
Small current, 10amps at most, means a small switch and wiring.
Momentary only as it will kick up armature amps and overheat motor in 60 seconds or so. More guessing!

Plaid setting is reserved for 8th battery install only


for the life of me can not figure out how to pm you

Fine Fine I guess Ill return this switch damnit lol. Put the money towards the extra long battery cables my thought was to wire all the new lights I got to that battery and then hit it when and if I needed it for the motor. But they are all led lights and I might have just over thought it slightly cough and wanted maybe a cool boost button cough cough lol.

Holy S*** B@lls batman! I added a 110ah Lifepo4 exactly the way you did and gosh darn does it make a difference. I experienced the -51 code as well but its only if I hammer it off the get go. If I ease into the throttle its smooth sailing. Im starting to wonder if maybe my gem has been programed or modified already. It was owned by a college before I got it. I just broke out my gps and up hill at full charge I hit 32 and leveled out 36 on flat ground for a min. but went down the road to test it on a road that has a very slight uphil grade for about half a mile and stade steady at 28-30mph with the battery reading 75%. Stock wheels and tires with just the battery add.

Now you are getting the idea behind this whole over voltage thing that goes on here. It’s amazing how anemic stock V can be, especially when the batteries get some age on them and V dips when under hard accel.

Be aware of running mismatched/mixed batteries tho. It makes for a complex pack arrangement. You are previously accustomed to running the car until it slows down to a crawl or throw a turtle. With the 7th battery mod you will be running one or more of your stock wet cells below the 50% threshold and putting it in the danger/damage zone and eventually killing your pack.

To be honest I dont like driving the vehicle under 65% battery. Although I did get a random -66 when trying to go up a hill last night with another code in reverse as well as -51. Few power cycles and I was good but a little worrysum.

-66 The field current exceeds the current limit of the field transistor.
This could be a sign that your motor is due for a service.

What motor are you running and when was the last time it was serviced?

-51 Capacitor volts are low before the line contactor closes.
Feels like a power up sequence issue. Might be due to flipping key Off/On too fast. It might also be seeing the shenanigans being run and not able to understand the extra battery.

yeah -51 happens when I hammer it from a stop sign which makes sense. I have to check the motor. It was owned by a college in vermont and serviced regularly up untill last year.

how dificult is a service

Depends on tools you have available, and your talent level.

At least pull the motor out of your car and get a look at it (you have to do that anyway to take it to the shop).