I don't know if this is Canon or not, but my Nikons you select which battery it uses first. So it drains one battery first, then the other.3) Give you two batteries instead of one with increased general battery life. A bonus always - but if you've only 2 batteries I'd recommend keeping one in body and one out so that you've always got a spare with you (better than having both inside and running out on both at the same time without warning).
Then I recommend this for GAS attacks ==> Beano® Prevent Gas & Stomach BloatingThanks all for the info and suggestions. I got a nice gift card from a friend with the instructions to spend it on my hobby and since I just upgraded my body and also got myself a new lens for Christmas... I was trying to figure out what my next purchase might be. I really don't need anything at the moment so I'm probably going to save it for my next GAS attack.