The DS has a Li-ion battery, it doesn't suffer from the same kind of problems that NiMH batteries do with constantly being used. NiMH batteries have a "memory" effect, being that if you use them to 50% capacity, then charge, and continue to only use them to 50% and charging, they will only be able to hold 50% charge over time (this is why you want to discharge NiMH every 1-3 months). Li-ion batteries do not have the memory effect, but I'm pretty sure that keeping your battery topped off all of the time will do some sort of damage over time to it.