Except that the battery is integral to the power circuit and if not functioning properly may cause problems; even if connected to the mains. Of course you could also have a suboptimal connection at the battery contacts or within the battery. The power switch could still be faulty, although this is unlikely at this point. This can be eliminated with all certainty by jumping the switch.
To be clear, I have observed the problem with two completely different batteries at this point.
Also, I have just verified that the unit did not reset on its own or otherwise stop working after being left alone on battery power for two hours.
"There is much pleasure to be gained from useless knowledge." --Bertrand Russel (attributed)