Might not be a problem and just some type of temporary glitch, so try playing your DS Lite till the battery goes completely dead and then see if the charging light come on when you plug in the charger.:)

And if it doesn't and/or the AC Adapter doesn't seem to be recharging your DS Lite then a person could go through some basic troubleshooting to determine exactly what the problem is and the best solution to it.:)

Such as borrowing another AC Adapter and then another DS Lite battery from a friend or family member to test on your DS Lite.:)

But try deleting the battery first and see if there is a problem or not and then we can go on from there to see what next you might want to do.