most battery widgets need to be calibrated. after a few charge cycles they give their best "guess" as to how much time/charge you have left based on your previous patterns. Also the battery indicator isnt that reliable. Battstat is a great battery widget that uses the system battery settings, or if you root you can get the battery percentage instead of the battery icon.

 

your stock battery indicator is way off. try batteryminder from the market.

 

I would guess that it just needs recalibrated, yes.

Although it may also just be that the stock can't be that accurate. I have another app replacing it so I can't check, but say the entire thing is four pixels wide. For 100% of course it'd have all four pixels. But it may wait until it's below 75% to only show three pixels. Until then all you know it it's somewhere between 75 and 100%. Same with three bars - it could be anywhere from 74 to 50% battery life. It's just that the app's size limits its accuracy.

 

I've found that the stock battery indicator is a little flakey. I use Battstatt and Battery Indicator to see the %.