Not OP: I charge mine while I'm in the shower and eating breakfast. That gets me through the day with about 50-60% to spare. I do wear mine overnight.

I have a relatively new series 7. It remains to be seen how it performs as the battery cycles hundreds of times.

edit: Fixed percent remaining. It was much better than I'd remembered.

I have to charge daily (but I wear it the rest of the day, including when sleeping). I usually do it in the morning after my workout as I start work.