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We replaced the AC/DC wall plug with a unit that outputs 15V 2A.
16.8V 1A 4s Lithium Battery Charger Adapter.
This one failed so we replaced with a 12v AC/DC power supply.
Installation
So, we added a buck converter to the input which drops the voltage to 12.9v to charge the battery and power the speaker. This buck module was simply hot glued to to the bottom of the board.
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