Charging problem—Acton s2

Hey all. How do you t/s if battery issue is BMS, ESC, or a the battery itself? When I get a voltage reading it is between 36v and 42v.

Here is the long story: Picked up an Acton 2 to tinker with. I am having an problem with the battery charging. The charger shows green like the battery is charged—but it immediately loses power when I disconnect. I pressed on the battery pack and got the charge light to go red for a while. Then it went green. Got about 400 yards and then it died. Then the press trick did not work. While taking voltage readings I unplugged the pack from ESC when I plugged it back in there was a little spark and it started charging. ? This time I ran the board and then I plugged it In—went straight to green. Tried the same trick—didn’t work this time. I am stumped!

As an update: I removed the battery pack from the case and load tested it with a carbon pile at work—it would spike it and then shut off. I feel like this at least proved them pack was an issue. I tried taking voltage readings on the pack at the BMS and got 16v most places but only 8v on reading. I need more understanding on how 10s2p packs are constructed. Is a BMS necessary for regenerative braking? If not I could purchase a battery tack welder for $80 and find the bad cell (and have it for future projects) or I could buy the whole battery with a BMS for $175.

In the mean time, I took what I think is the temp sensor and moved its position. Then I left it on the charger (by accident) for a week. I came back to it yesterday and it runs like a top (it runs great).

Put it back together and test drove for 1.5 miles: no issues. Longer test drive to come soon.