Help ibook dies unexpectedly and often

It started just a few times and now it's dying once or twice a day in the middle of using it.
At first it was like it was still on but the screen was dark.
now I have to use the control button to turn it back on and it comes back on but hasn't shut down.

I tried resetting pram and did the disc utlity repair and it said the logic board, etc was fine.

Any suggestions, I am going nuts!

battery

well i do need a new battery but I keep it plugged into the wall . It holds a charge for about 30 minutes.
I use an igo plug in charger often now because I wanted a car charger and the igo seems to stay snug in the ibook. The apple adapter seems to become loose often and I have to toggle it to get the charge going again.
Do you think that might have something to do with it?
It always says "battery low" if it needs to be plugged in more securely so I am thinking it isn't just dying out of the blue w/out a message.