Windows 7: rapid battery loss to a black screen

Often times while running some software/hardware on battery
The battery life will be between 50 and 60%
suddenly the red battery icon lights up and the monitor goes black
the computer is still on and running but it's as though the monitor shuts off
there is no way to get it back even when i plug it in immediately

I have to turn it off
when it starts up again the battery life is low around 5 to 10%

I'm not sure why it says around 50 with an hour left then suddenly it's so low
i've also noticed it is kind of chaotic where it might say 1 hr left and then in a few minutes say 2 hours left

but the unexpected loss is what i'm wondering about
obviously i should keep it plugged in
but i wanted to check if anybody else experienced this

It is probably the battery. If your computer has a calibration feature use it. If not take it to a computer shop and have it tested. Or just replace it


Ken