I would add that Marty frequently warns that if any PS1 or early PS2 locos have a white battery, do not power up but immediately discard the battery and replace. If what I say is wrong, I'm sure Marty will correct me.
I have replaced all my PS2 5-volt boards with 3-volt boards, have upgraded all of my conventional/PS1 engines to PS2, and have replaced all of my batteries with supercaps.
If one uses 3-volt PS2 engines frequently, there is nothing wrong with a battery--mine lasted 8-10 years.