I have an MTH Railking GP-7 (30-20008-1) with the original battery that has gone bad. The battery is in a bad spot located under the PS2 board and secured on all sides by the metal frame that supports the PS2 board. You pretty much have to pull the board and wiring to get the battery out for replacement. Why they didn't just leave one side of the retainer clip off so that you could just slide the battery out is a mystery to me, it sure would make this job easier.
There is room in front of the battery to fit in a BCR, but is it wise to leave the old battery in the loco?
H1000