I had a dead rechargeable grip. The handle is easily disassembled by heating with an industrial hair dryer from the side of the slip rings. First you need to unscrew the side spikes for charging. Most likely, judging by the size, there are 18650 connected 3S4P inside. You have to be very careful with the driver (last picture), the wires (jumpers) are held very gently and can be removed from their attachment points. We'll have to tinker to determine what flew off from where. And then just replace the batteries with modern ones