My HP DV6 1106ax laptop with Windows 7 64-bit is about two years old. The battery died recently - it wouldn't charge and would turn off as soon as I unplugged it from the power. 

I bought a new battery the other day which worked perfectly on the first charge. When I first put it in, it read about 80%; I charged it to 100% then unplugged it and ran it flat. 

I then plugged it in and left it for a while. When I turned it on it said the battery has 43% and doesn't get any higher than that. If I unplug it from the power the laptop dies.

Does anyone have any advice? I find it strange that it charged up and ran off the battery the first time I put it in but now it won't work. I've tried reinserting the battery to make sure it's sitting right and all seems correct.