How to change an amp to put batteries in it

Three strings means there is grounding.

Grounding shields the signal from interference and also stabilizes the potential for government and work.

Ground wire just soldered to the amplifier shell.

The easiest way to change the battery input is to buy an amplifier board. 12v choose TDA2003 mono amplifier, 8 ~ 10W output price of about 10 yuan, the input is connected to the original speaker jack, the output is connected to the speaker, modification is easy. And do not destroy the original circuit board