Awhile back my standard ep121 charger failed, I got a replacement from amazon and all was good for awhile. After a few months the battery quit charging, regardless of if the tablet was off, in bios, or in windows. I've upgraded the bios (and replaced the bios chip). The battery looks physically fine but I have no idea how to test the battery and or charging circuit. I've ordered another charger just in case that's the problem.