TYpes of battery for E70 X5 3.0i
 

The onboard computer is complaining that the battery charge is running low. It's an 08 X5 3.0i. While I'm not particularly thrilled, for a relatively small city where I live w/ plenty of stop & go traffic and little high way driving, it really drians the battery FAST!

So I called up the dealer and was slightly confused about the BMW factory batteries options:

White colour one w/ 90ah and 720A
Black colour AGM one w/ 70ah and 760A
Black colour AGM one w/ 90ah and 900A

The 1st two are similarly priced while the last one is abt. 25% more so I'm just wondering if it's worth it to go for a better one or this would be pretty much the same?