USB Nintendo DS charger?
Here's a idea my head came up with Look at photo, See?, DO THIS ON A OLD DS THAT YOU DON'T WANT ANYMORE! NOT MY FAULT! IF YOU GET BLEW UP OR SOMETHING! DO IT AT YOUR OWN RISK! OK no more of that :)
USB 2.0 outputs: 5 Volts
DS output : 5.2 Volts
Maybe a slower charge? What do you think?