if you take off the charger, and still there is an issue, clean the battery contacts on the psp itself. (use a q-tip with a TINY bit of alcohol) rub it very rigorously.
also i would suggest cleaning the contacts on the batteries.
another thing is that if you recently took it apart and put it back together, depending on the series of PSP you have, there could be a wire under the plastic riser bar, or the R trigger is not set in correctly (possibly also the R trigger guard in the 2000 series)
hope that if the problem does return this helps.