Are these helmet headsets salvageable?

[juntjoo]

These both died after charging them. I might have used a different charging cable that caused this to happen. Idk. Maybe they just suck. They're over a year old and I didn't use them that much during the time. They were stored in my garage the last 7 months or so though so maybe there's more moisture out there that caused damage.

 

[dave9]

It looks like there was water soluble flux residue left behind after manufactured and it was too damp so that formed conductive shorts, so I would scrub the boards, especially where you see the residue, with hot detergent solution, then soak and agitate, then rinse with alcohol, shake and let dry for a day before trying them again... maybe the shorts caused damage or maybe it was only temporarily interfering with function.

You wrote "charging them". Don't get the battery wet (nor the board with battery still connected) it may need removed for cleaning or possibly it is just dead. You could try an alternate (3.7V?) power supply to see if the boards still function.

If they were stored with Li-Ion batteries drained too low, it could be a protection circuit preventing charging, but if too low they may be damaged now and should be replaced, so knowing if the boards still work with an alternate PSU would be worthwhile before going to the trouble/expense of replacing them. If they're around 2.5V or more, I might try an alternate charging method to push their voltage up some, then see if the built-in charging circuit with the USB supply as intended will charge them.