I have the same batteries and charger as you do. I only charge two batteries at a time as I wasn't sure, like you, about drainage when not being used. As these are NMH batteries, they apparently don't suffer from the deterioration in performance that nickel cadmium batteries do if you charge them before they're completely empty. I have, in fact, done this on a couple of occasions and still got the same amount of life. Just my thoughts. No doubt someone else will correct me if I'm wrong.