Why my speaker is not powered?

Hello guys,

First of all I'm not an english native speaker so sorry for the mistakes.

Couples year ago my UE BOOM 2 fell into sea water and it didn't work anymore, when I get home I just put it in rice and and it stayed in for a very long time. 2 days ago I tried to charge it (there is the blinking white light) and to turn it on and it worked for like 30 seconds I was able to put music and then it turned off saying that there was no more battery. Basically every time I plug it and I wait a bit I can turn it on during few seconds. I managed to unplug the battery (Li-ion 3.6V 3200mAh) and tested it with a voltmeter. It says that the battery voltage is 4V, then I concluded that the battery was fine and there was an issue with the powering of the speaker. My questions are : have you ever seen something like this ? Do you have any advices about the pieces I should test or replace ? Does anyone know how to fix it ?

Thank you