I have replaced the battery in mine two months ago 2005 with 92,000 kms I used a commodore battery from R&J batteries $120.

( I can post the number if anyone wants it)
I was trying to find out why my lights would flicker constantly, Had the alternator, and engine control computer replaced The regulatior is in the computer in these cars)all under warranty to no avail.
The lights got so bad that when I follow someone they thought I was flashing them (with my lights!!!)
I told the dealer on two occasions that I thought it was a weak battery and they fobbed me off.

Well the good news is it was the battery and just think I had to put up with the crappy flickering lights for almost three years.
Now everything is as it should be.
One of the problems I had for a long time was that if I left the radio on while I washed the car or somthing like that it would flaten dthe battery, but I never had trouble starting the car any other time.