BG-E3 Battery Usage Question...

So, I've wondered this for the past 2 years about my BG-E3 but never got around to asking.

Say for example:

I have both NB2-LH batteries in the grip, both fully charged, and I do a shoot of only say 100 pictures. BUT tomorrow, I have a shoot that will probably use up most of what I have left, if not more. I dont want to waste time and burn out the batteries by charging them both if only one of them got used.

My question:

Does the battery grip use from both batteries equally at the same time, or do they only use one battery at a time, and if that's the case, which one?

Does anybody know?

Thanks!
~Jonathan

Yes, it draws from both at once.

That's obnoxious...but I really appreciate your answer.

I've also noticed that the battery indicator is not always completely accurate. If youre shooting for 5 hours straight, it says full battery until about 3.5 hours in, then it goes down to 2/3rds then a few minutes later 1/3rd and dies shortly after.

I've gotten it timed out pretty well but it was upsetting when I thought I had full battery for quite some time then moments later nothing.

Thanks again!
~Jonathan

That's the power curve on Li ion cells. The voltage is fairly stable most of the way through and then drops rapidly.