Marcus Jenkins made a capacitive battery charger using Dirty Board PCB’s to revive rechargeable batteries:
This is really a basic, bare-bones circuit. I’ve prepared the PCB with a view that it could be used as a module in a rather more-sophisticated charging system. You could imagine using a microcontroller (e.g. Arduino, PIC, etc.) to monitor the battery voltage and disconnect the mains input to the charger module when voltage reaches a user-selectable limit. The microcontroller could also have a thermistor probe to attach to the side of the battery with elastic – a basic precaution to try and automatically disconnect in the case unreasonable temperature rise while charging.