It's only the Revo map that defaults to a reduced performance mode if the battery is pulled. You need an SPS switch to re-enable the Stage 1 map, or a trip to a Revo dealer.
If you don't have a Revo map, pulling the battery won't affect anything.
As above, the battery doesn't need disconnecting to change the belt, but a lot of garages do it regardless as a precautionary measure.