If you are rooted, you can use a custom battery icon on the notification bar that displays the percent instead of just a the bars. Or maybe an app like this: Battery Indicator

 

The app I linked to puts the percentage in the bar at the top of the screen (check the screen shots). While it's not that large, it would give you a more accurate indication of your battery level. The status bar is visible on the lock screen, so it should do what you need it to.

As far as having it on the actual lock screen, I only know of widget locker, which I too had problems with on the Eris. Not enough power to keep it running all the time.