You can recharge them pretty easy but you won't have any kind of overcharge protection. Just get a wall wart that's about 6 volts and put a 6 volt light bulb in line to act as a current limiter. and connect the hot and ground wires to the proper ends of the battery. You can make a tray and line 4 batteries up in series and use a 9 volt or even a 12 volt wall wart to charge a bunch at one time. Don't forget to put a 9 or 12 volt light bulb in series to limit that current. Make sure the wall wart is DC volts because Some are AC and are rectified in the p[iece of equipment they were made for. HINT: The lightbulb will glow when you start and then at a different brightness when they are fully charged. As I recall, they glow bright at first and then get dimmer as they batteries get full. Its been a while since I did it so it may be the other way around.