Over in Howardforums there seems to be discussion about batteries ending in "31" not lasting as long as those ending in "20" which seem to be the replacement batteries. My battery is DC081105 out of the box and I got the phone about 2 weeks ago. I use mine mostly for email and the battery lasts all day but I'm not a heavy user of battery.

Does the problem seem related to the serial number on the battery or is it more of a usage issue.