Sony PRS 600 formatting problem

[slapperuski]

It seems that whenever I enlarge the font on my ereader to Large it takes several minutes to format. Should it not be almost instantly? Also, my reader freezes and then goes into format mode and eventually totally freezes. I can reset, but then when I go to return to the previous page it again freezes in the Large font, but it will allow me go go to the page in small font. All problems seem to have started after charging with a wall charger I bought off of EBay and not using the USB method. Does anyone else have these type of problems? Any ideas? Is my battery possibly defective? Please help, thank you.