Battery upgrade questions

I recently bought an Acer Extensa 4420 and while I like most everything about it, one thing I don't like is the battery life. It came with a BTP-ARJ1 11.1V 4000mAh battery which gives me between 2 and 2.5 hours with wifi and a few programs running (undervolted with RMclock and with Vista Battery Saver). I would like to buy a second battery but would prefer to get something bigger that would give me more run time. I found this one but am not sure if it's my best bet.

As I don't know much about laptop batteries, maybe someone here can clarify...

1. I see replacements for the BTP-ARJ1 that are 4000mAh, 4400mAh, and 4800mAh. Anyone have an idea how much better the 4800mAh battery would be as far as run time?

2. I was thinking about getting a 9 or 12 cell battery but haven't had any luck finding one when Googling BTP-ARJ1 and 9 or 12 cell. Do I need to get something compatible with this Acer part number so it "fits" my notebook?


Thanks for any help with this!

Andrew

 

The Math says 2.4 to 3 hours with the 4,800 the way you use.

 

Thanks for the info powerpack.......how do you calculate approximate runtime from the mAh capacity?

 

You don't exactly. But you said 4000 mAh gets you 2.5 to 3, 4800/4000=1.2. Multiply your #'s by that and you have your answer mAh won't tell you time on it's own as you do not know the power draw, but all else being = my estimate should stand if your estimate was correct.