If you are handy you can build a LiFePO4 battery pack for close to half of what a shelf product costs. And, you know what you have. I built a 48v for my golf cart for about $900. I had a SS box made on Alibaba and a JK-BMS. 16 cells 100Ah produces around 58v.
I noticed several comments snout BMS size like 200A. But is that continuous discharge or Max Amps? Mine is 200/350. I have a lot of hills. I hope that’s enough.
So I got the 6x12v battery pack installed. She is alive! However, I think the cart is confused since the pack is different. Not sure if I need to change any settings on the charger. The pack is 105ah, compared to the 140ah 8v pack that was originally installed. Also, it was a military fleet vehicle and it does not go into DH. So, not sure if that would be a programming deal, or, if they disconnected a wire somewhere? Her top speed is roughly 10-15mph at this time. AI said that if it’s a smart system, it will figure it out and get the battery readings right after a couple full chargers. But AI is not always right… Do I need to do the charger settings change by connecting and disconnecting the battery cables until it goes to a new charging preset for the lower AH?
If the drive select switch moves from Rev to DL, and it doesn’t make a difference when switched to DH,
What actually happens? Does the dash indicator bubble stay on DL?
Or does it actually move to DH but the car does not go any faster?
Are there any other odd lights on the dash display? Perhaps a temp or a turtle light ? These are two things that would keep the car from going faster.
Also, depending on how long this car has been sitting, the odds are good that this motor may need servicing.
Is the car running smooth? or is it jumpy when going slow?
It has 4 brushes. If one of them is stuck and not making good contact, then you are only working on half a motor.
Plan on visiting all four corners (wheels). Check the brakes to make sure they are not dragging and not leaking after a hot lap around the block.
Make sure your tires are in good shape and properly inflated.
So I got the 6x12v battery pack installed.
What batteries did you install? You may need to change the charger profile to not damage these new batteries. This is not keeping you from going faster, but something to think about.
When I hit the switch to DL it moves to DL. When I move the switch to DH, it does nothing new. It stays on DL.
I noticed the only light on was the seatbelt light. No other lights present. The cart runs smooth at low speed. No grinding or scratching coming from the brakes. It definitely feels like it’s being limited due to the DL setting. However, they are fully charged and the battery on the gauge shows red one bar. I will check the charger algorithm tomorrow to see what it’s running at.
Ok, then the clue is in your original thought. (where this car came from).
The original owner(military) may have jimmied it so it would only stay in DL. If the bubble never moved to the DH then I’d say different.
We need to explore how they did it.
Oddly enough, I think I remember there was even a factory solution/lockout offered. Is there a second key switch somewhere around the steering column?
If nothing obvious, Post a pic of the 23p harness/connector up on top of the motor controller. Let me have a look at it. Specific attention to pins 4, 5, &6.
Otherwise we need to pull the dash panels (upper and lower), then the dash pod cover to get a look at the back of the Drive select switch.
Here is the pin connector. Also, I was thinking about the dash and the battery percentage available. Wondering if I did not hook up the bridge wires correctly. I hooked up the cart - to B1-, Cart + to B6+. The 250a bridge - wire to B3+, Bridge + wire to B4-. Don’t be too hard on me if I am wrong lol… Never done this before, plus I could not copy the layout from the previous 8v setup, since I’m on 6 12v’s now. PS… cutting my nails now.. I know, I’m a caveman. 
I was thinking about the dash and the battery percentage available.
Don’t worry about the SOC Display at this time. I skimmed over that for now because the SOC/battery bars display is not what is keeping you slow. There is a chance it will fix itself after a few charge cycles or it can be manually reset when car checks out.
I see the Main harness connector on top of the controller. Thanks. Now follow those wires up a bit until they disappear into the harness. Look for any cuts/splices/taped up mayhem that does not look original/factory.
This is the first/easiest place to lock out DH if you know what you are doing. If all looks unmolested, then we need to look at the back of the select switch. It is not too difficult to remove the dash plastics.
Did you look for an added key switch? I believe it would be in the pod/column.
Here are the internals. I don’t see much Tom-fool-ary going on. I also don’t see anything additional on the column for a seperate key. I also added a photo of a bunch of wires not attached in the battery compartment area.
Thinking this may be programmed into the controller?
You are close.
Can you figure out how to remove the backside of the dash pod cover?
Unfortunately, you need to remove the lower dash panel to get at the bottom screw.
Then get me some pics of the front and back(wiring) of the Drive select switch.
Sorry if I’m taking a bunch of photos that don’t help! Trying to get all the angles. Also, I noticed one screw missing from the steering column 
.
Looks like that yellow wire double backs into it, not sure if that is normal.
I fixed it. Thank you for working through it with me! Just connected the blue wire into a slot. High is low, low is high lol. But it works great!
High is low, low is high lol. But it works great!
Well there ya go.
If you want to fix that. Swap the Yellow and Blue wires on the switch.
(not the yellow jumper)
Yes, you absolutely will need to change the algorithm setting on the charger or you will slowly kill those new batteries. The 8v vs 12v is not relevant, as it’s still a 72v pack and it’s a 72V charger. The problem is the battery chemistry is different, way different. Those Polaris 8V batteries are gel cells. the Duracell SLI31MDC s a Flooded Lead Acid battery (aka “FLA”). Gel batteries and FLAs have very different charging profiles, the short explanation is that charging FLAs with a gel setting will result in undercharging that, besides simply not giving you 100% of your battery capability, will cause the more rapid forming of a non-conductive layer on the submerged lead plates, as this forms, the battery becomes “weaker” - less able to store and pass electricity and will fail prematurely,
You are going to need to chock the rear wheels, and put the front end on jack stands, and watch the blink code on the charger as you first power it up. You may be able to see what you need by taking off one of the front wheels.
Being government surplus and possibly having been purchased w/ different requirements than what the stock civilian models come as, we can’t be 100% sure if the charger still has the typical algorithms installed, I would recommend you find out what it’s set to and check a couple charts to see what matches, from that you can kind of pick the one you need to switch it to.
If it’s the vanilla gem package, factory setting would be 14 maybe switched to 24. For that, switch it to 32 for the FLAs you bought. The battery pictures you posted show a date code that matches the model year of the vehicle, so hopefully it’s the stock charger programming and no one dicked with it.
If you find that it’s set to something else, there are so many possibilities, best to just post it and we can take some stabs at it then.
Links for the PDFs on how to check / change algorithms and the stock GEM programming are below.
User manual:
https://support.delta-q.com/hc/en-us/article_attachments/360012713231
Stock GEM algorithms list / instructions:
https://support.delta-q.com/hc/en-us/article_attachments/360012712932
BTW- those SLI31MDCs are really good batteries for the coin. Built by EastPenn Deka in the US and they use virgin lead rather than recycled. You need to check the water periodically - depends how much you use it. Once every week or other week until you get a feel for the rate it drops by. Avoid the Trojan flooded battery profiles if you can, they can be pretty brutal on mere mortal batteries. Trojan batteries are kind of in a class by themselves, there’s over 50% more lead in them.
The battery cell water caps are under the circled sticker in the photo below. It should peel up pretty easy. The best tool I’ve found for unscrewing the recessed caps that EastPenn Deka uses is a bartenders speed bottle opener, the bare metal ends have near perfect curvature and width to fit the slot in the caps so you can unscrew them without chewing the caps up (they are soft plastic).
Here’s a link to download the Operator’s manual for the 2015, the 2010 isn’t much different in these regards.
PM me your email address and I’ll email you the maintenance / service manuals for both years. As it’s against forum rules to post them here.
Lastly, if you haven’t already, make sure to save the extra battery series connection cables and hold down brackets that you didn’t reinstall when you went from nine down to six batteries. I’ll explain why later after you have the cart running & reliably drivable on the street..
Amazing information! I will get on my coveralls, setup a FaceTime video between two phones (one under the hood watching the blinking lights), and find out what algorithm I’m on! Thank you for this!!
That was easier than expected. If only those troops at this cars past life knew how easy it was to get those security star bits, and plug in one wire lol. 
