Plausibility of ancient extraterrestrials

[Gawdzilla Sama]

Batteries imply a technically knowledgeable infrastructure. They don't just float around doing nothing on something.

Not really.   It only imply knowledgeable infrastructure if its principle of operation is known well enough for it to be adapted to multiple uses requiring different currents and voltage.

They would be making the damn things for a reason.

Otherwise it could simply be an accidental and superficial discovery resulting in a curious artifact that does not form, nor imply the existence of, any foundation that could be built upon to anything significantly more.

Yep, dropped from a flying saucer, no context allowed.