the battery’s in these units are junk. you take it apart very easy just 2 screws and you will see the battery it is in like tin foil very small. you can find battery’s like this in old cell phones / bluetooth headphones / many small electronics that are rechargeable. there is a red and a black wire . if you can solder just solder in the new one if you can solder just bare the wires and twist the red together and same with the black and put some black tape over them so the don’t short out. charge for a good 8 hours and your set good luck