I replaced my laptop (HP 6735s, Windows Vista) battery about 3 months ago due to its poor performance (it was running out after about 20 minutes).
The new battery (some cheap one off eBay) that I had seemed to be working fine, but because I hardly ever take my laptop off charge, after a few days using it, I let the new battery fully discharge and kept it in a drawer. About two months later, I needed to use the battery again so I charged it fully and started to use it.
At first everything was great, and I was up to 50% charge after 2 hours of usage, when a small red cross started flashing next to the battery icon. I received no other messages or notifications so I was confused as to what this cross meant. My laptop and the battery continued functioning as normal for another 15 minutes, but because I didn't know what the cross meant, I decided to plug it back in (and the cross symbol went away and was replaced with the charging icon) and turn the laptop off.
I'm assuming this is a fault in the battery, possibly due to me leaving it in the drawer for 2 months. Does anyone know what this icon means? And if it is my battery, is a replacement the only option?
EDIT: The drawer which I kept it in is right next to a radiator which is frequently on :\