I have a Sony Vaio laptop (VGN-TX750P). After not using it for a couple of months, I found the battery (apparently) dead. I plugged it in, and it came on. I saw that the battery light was doing a cyclic double flash. After being plugged in for over an hour, I unplugged it to move it, and it died instantly. I assumed that the battery was history, so I purchased one online. Guess what? Same situation with the new battery. The computer runs fine on the power cord, but it's as if there is no battery there...
Never mind... after charging for a period of time, it seems OK!