I had 3 batteries for my D70s at the very beginning, then 1 quickly died and wouldn't charge or give off any energy at all. Just recently my second battery did this as well, but it will last a whopping 1 minute unlike the other completely dead one. Now i am down to one battery. Sometimes before going on a trip i will pop it on the charger knowing that i used the camera a little bit, and i didn't want the battery to die on the trip. Is it bad to top off a battery if it isn't dead, or if it still has 3 bars?