Can’t imagine the 500 charges are spent yet, but if you somehow have managed to deplete your Nintendo DS battery, then here’s some good info. lik-sang has taken apart a DS and has some interesting information about it, including replacement battery power:

If you cut away the two small plastic pieces of a standard GBA SP battery (see pictures), you can use it with your Nintendo DS. This is of course only recommended for people who know what they are doing, but this might solve your temporary power issues if you are waiting for some first party batteries to arrive, or if you already have a bunch of GBA SP batteries. With this piece of info the last power-related question importers had is now also answered.

I’m still working on the original battery charge, so I’m good to go for those 500 or so more chargets. BTW, Lik’s pictures are a lot better than my sucky DS pictures.