4.4 Battery Replacement (?)

[159night]

I'm new here - so be kind I'm on my 3rd X5 and love them. This 2006 4.4 has been great except for this odd starting issue. Acts like a dead / dying battery, but the dealer says its fine, resets a few things and send s me on my way. Anywhere from 1 month to 6 months later I'm back. Last time they called in the BMW rep to the dealership who had them replace the 'brain', one week later gave it back and worked for almost a year. Now I'm back again with the same issue. 3 days later I get a call saying its the battery and they want $410 to replace it (?). Really, it took 3 days to put a load test on it? http://www.xoutpost.com/images/smilies/loco.gif

Basically I'm not convinced it needs a battery and IF it does, where can I find a quality one for a more reasonable price? What is the cranking amps needed?

Thanks!