Get a plug that has a positive and negative on it strip it so it’s got bare wires on it then make sure thr plug your using has between 6/12v anymore than that could be very dangerous hope this helps then put the wires on the plus and minus of the battery for 30 secs to a min and it should work I think the left side of battery is negative and right side positive 👍
Faulty battery sir, the battery lifespan has ended. This always happens to old batteries. I will do what you have suggested before replacing it with new batteries.
