I dunno abt the ds . but for my psp i just charge until its full and take it off.

Even when i leave it on standby the battery dosent go down , say abt 1 to 2 percent per few hours ?

If i turn it completely off then um, i can leave it there for a few days and have a more or less full power psp . definitely > 90%

Most of the time at home , i just leave it charged over night then i go to uni the next day. So far my psp batt life shows no problems.

And yeah, when im playing the psp alot at nite, i normally plug it in so tml ill have a fully charged psp for uni . XD .

Normally, my rule of thumb is , dont charge it unless its below 50% . I dont know if it works but so far like i said my batt life shows no problems. =D