Be very careful with electric vehicle wiring. It can deliver enough high voltage DC through your body to cook you crisp. Don't charge anything without a current limit. Batteries can make an explosive mix of oxygen and hydrogen. Put a spark next to that and detonate battery acid straight through all your gristly shreds.
We bought this Gem Electric Car for very cheap because it wouldn't drive and wouldn't charge.
Its six 12 volt batteries were all sitting at less than a volt, and were probably shot.
The price of the vehicle reflected these factors.
When we got it back I jumped it to an external 72 volt vehicle pack to see if it would move.
Sure enough, it moved fine. Not only that, when I plugged the AC charger in, a green light started flashing on the dashboard; it was charging!
Apparently the charger has a safety feature where it doesn't even try to charge if the pack voltage is too low.
A few months later (today) after a flat tire and some sitting, the gem car wouldn't charge again and the batteries were flat dead. This time I woke it up in a safer way. I jumped it to my 36 volt golf cart charger. After a few minutes I disconnected that and plugged in the Gem car. Abracadabra! It's Charging!
And what about those "shot" batteries it came with?
They weren't bulged, which means not badly sulfated. On the first charge it was barely able to drive a mile. Then each time we charged and drove it it got more range. I asked Otmar Ebenhoech
(EV guru) about this and he said that the high charge and discharge currents of electric vehicles desulfate them. Batteries in an EV that is actually used do not die from sulfate, they die from overuse.