Sometimes the voltage regulator on an alternator can go faulty, thus not actually regulating. This can mean excessive voltage which "cooks" the battery and reduces its' life.
Ironically I had a very similar problem this morning - car wouldn't start; had to jump start it. Was driving to work and the power steering stopped working, ABS light came on, Airbag light came on - I thought the dash had turned into a Christmas tree!
I quickly decided to go to a garage and got a new battery. All seems OK now. On checking the voltage across the new battery, I get 12.35V engine off; 14.25V engine running. These seem to be within spec from what I can find.
Hope this helps. :-)
Ian, Scotland.
February 2010