I recently acquired a PS2 set (MTH 30-2774-1) for quite a steal. I'm still learning my way around the functions of PS2 as I typically stick to more analog locomotives. All other PS2 engines I've purchased before have worked so far but this is the first that requires troubleshooting.
Using a Z500 transformer, I set the engine on the rails and ran it for ~15min to test the battery. I received no sound during that time and I checked to ensure the volume was turned up. I then tested the couplers, motion, and smoke unit. At a few points the sound would randomly pop in but then disappear again. Based on noises I am hearing, it sounds as though the speaker is on, however no sounds are being produced.
I know PS2 engines use the battery and that is the cause of many issues, however I am not entirely sure of the function of the battery. Would other functions, such as coupler control, still work if the battery was bad? Or is the lack of audio a fair indicator of the issue? I plan to open this engine up in the next few days to take a look but I wanted to get an idea of what may be the smoking gun (aside from a pinched wire or something silly).
I've included a video below that has the engine power up into neutral, then power down until I hear the battery cut out after a few seconds. Thanks!