Weird , the orginal poster states his battery was doing GREAT using the usb cable until feb , THEN HE SWITCHED to AC charger , and he developed problems with battery. Duh! Am I missing something. Maybe he should go back to the usb charger if it worked for him. Maybe the AC is screwing up his battery.
Now if you tell us you went back to charging with usb and it still doesn't work right, then yeah maybe that "AC charger you were using ruined your battery. Trouble shooting , 101, see if it's the AC charger, or the ereader battery, by going back to what worked for you in the past. Is it that you can't use USB anymore? Get a PSP battery charger if you want to go by AC.