2003 GEM, Ride4fun upgrades (T5, motor, gear set, tires/rims and electrical wiring) and 6 72v Allied 18ah lithium batteries (3 years old) with meter and shunt. Cart does 45+mph on level roadway.
Need to pick everyone’s brains on this one.
Drove 8 miles and rested cart for 2 1/2 hours.
After 4 miles driving home, every thing shuts down including the battery meter which is directly connected to the batteries.
Plug in cart to charge for a moment, unplug and batteries are showing 77 volts. Charged for 30 minutes then drove home the additional 4 miles with no issue.
Plan is to run the car off each single battery at top speed to see if there’s any issues.
It is the opinion of many that hang out in this group that multiple 72v batteries in parallel is a design that will eventually fail (72v in a 6P). I am very surprised that it took 3 years for you to run into the issue.
Hopefully those Allied batteries all are monitored by their own internal BMS.
Is sounds like one or more may have gone offline/left the chat. There is no way to tell which one it might be without unhooking and testing each battery to see if it still has an output. I doubt your car will work with only one battery hooked up at a time.
It would be great if you had BT access so you could check condition of each battery while they are still configured.
I totally agree. You are seeing the biggest problem. There is no way to know how many batteries are pulling their weight. I suggest 6 ammeters, if you plan to keep these.
That sounds like classic BMS protection kicking in due to voltage sag under load—especially after a rest period where surface charge may have recovered just enough to start the drive.
At 3 years old, those Allied 18Ah packs may have one or two weaker cells dragging the rest down. Running each battery individually at speed, like you mentioned, should help isolate the culprit. I’d also check voltage drop under load in real time if you have a data logger or a buddy with a handheld meter and quick reflexes.
Have you noticed any imbalance when charging—like one battery topping off early or lagging behind the others?
Let me know if you’d like a follow-up message if someone replies with technical data or specific battery behavior.