Won’t turn on after water damage

I got this speaker on ebay and previous owner says it is water damaged. Apart from the rusty USB port (which is use to charge other device) everything look super clean and no sign of moisture. I hook a 11.1 VDC source to the jack where battery connect on the board, but it won’t turn on. Connect charging adapter (15V) and also no sign of life. Do you have any idea what should I check further to identify the problem and fix it. Many thanks

Rusted USB port