Every Acorn Machine I have with a battery has had the battery which has gone dead and leaked which has damaged the board.

I would recommend that unless the machine is going to be used every day the battery should be removed.
Hint: Its easier to cut the legs on the battery rather than unsolder it. This also has several advantages as you can solder onto the legs in the future with less risk of damaging the board and you can still unsolder them in the future if required.
- Open the machine
- Remove all the Case Slices
- Remove the power supply
- Remove the motherboard
- Remove the dead / leaking battery
- Wash with Vinegar (This cleans any leakage)
- Wash with Water (This washs away the vinegar)
- Wash with Methalated Spirits (This washs away the water)