Honestly, with as many problems as these things have given you, I would say it’s not even worth it to try and fix them. It’s likely you will just run into the same problems again. I imagine trying to fix these things will be a bit of a pain in the rear. If you are really set on trying to fix them, you might be able to find a battery for them on Ebay. I would guess the battery is probably solder in so that’s something to consider.