Battery change - '98 2.5 Boxster

Thanks Mel, but on the car's manual it says clearly NOT to use another kind of battery, because it may not produce the same results even if the same electrical and physical specs - in this case 12V 70 Ah 340A.

I know Porsche doesn't make batteries - of course! -, but since the car is still under some warranties, I was just wondering if any of you guys had some experience on this, either with a Boxster or a 996.

Thanks again,