On my 7290 I found that if it charged for around 8 hours and unplugged just prior to usage, the battery would not last as long as if I charged it for 2 hours just prior to using it for the day. I can see through my built-in battery gauge (bluetooth) in my Chrysler 300C, that the 2 hour charge just before usage keeps the battery gauge at 100% in the car when I first connect, whereas if I charge for 8 hours just prior to usage, the battery gauge in the car shows around 90% full. I believe this is due to the fact that the device never truly goes to sleep even when off and though the charger stops charging once you reach 100%, it likely never "tops off" till the charge falls down to somewhere around 90% or so. I have notice that talk time and general battery usage is definetely much longer using the 2 hour charge just prior to usage technique. I have tested this "theory" many times now and I can't think of any other reason why the shorter charge works better for me. I would imagine that the 8700 works in the same way too.
At least 17+ different BB's since 1999 -- too many to list...