Lionel Tinplate 392 Steam Locomotive Operator's Manual page 15

Replace: If the sounds are not improved at the end of the 15-minute test charge,
it is time to replace the battery. The battery is located in the tender. Remove the
tender shell for access to the battery. The battery is available through the M.T.H.
Parts Department.
DO NOT substitute alkaline batteries for these NiCad batteries. Using alkaline
batteries in this system can result in damamge to the PS 2.0 circuit board and/or
the batteries.
**Do not use alkaline batteries for testing or checking purposes for the 3-Volt PS2
boards. Using alkaline batteries will damage the 3-Volt battery charging circuit.**
Once boiler is removed, you can access the battery.
Battery port
Battery
Battery Location
Tinplate 392 Steam Locomotive 15