I had a really similar issue happen to my EMS cart when I first got it. If you look at the battery housing there is a tab that connects it to the circuit board on the south side of the housing (North being the top of the cart). My tab was unsoldered to the board and was actually positioned above the contact area.
To solve the problem I just took the... solder blob? and re-heated it while holding the battery contact against the circuit board, this melted the solder back onto the board and fixed the battery housing into position. Now the cart always holds saves and I haven't had any problems with it.
I didn't even have any soldering experience when I attempted this and my soldering iron was actually a woodburning tool that had a soldering iron tip you could attach. So even if you're hesitant to try because you don't have experience either I wouldn't worry about it since it's a really easy procedure.