I've had mine since July 2006.
I charge it just before working a long weekend. I work 3 twelves every other weekend and don't want the battery to die on me while I'm at work
. I'll also charge it if it shows less than 6 hours for when I work two twelves during the week.
Otherwise, I just let it go until I remember.
I remember reading that the battery does not like sitting at 100% charge for any length of time which is why you won't see it at 100% too often. The charging system is smart enough to bring it to 100% then to discharge it just a bit to bring it down.
Michael