Battery Drain

Thinking of getting an IS lens and was wondering what the drain on the batteries is like. I have a 400D with grip. From what I can make out even if you have two batteries in a grip, the power is drained from one battery at a time, correct me if this is not the case. I have a spare battery which is always charged, mainly to save waiting to charge both before venturing out again, so maybe buying another one would be worthwhile. But if anybody does know what effect using an IS has on the batteries I would like to hear.

Thanks

First, according to the 'manual' for the 400D grip (for 'manual' read slip of paper) the batteries are used simultaneously. Secondly, using IS does have an effect on battery discharge rate but not enough to be a cause for concern in my experience. Batteries are so inexpensive why not buy two more batteries so you can keep two in the grip and two spare?

When I had my 28-135, I used IS all the time, and really did not notice a big drain. Battery never died on me, even shooting for most of the day.

Back in the day when I had an IS lens (17-85 IS) I didn't notice significantly less battery life using it over any of my other lenses.

gofer wrote in post #6480668
First, according to the 'manual' for the 400D grip (for 'manual' read slip of paper) the batteries are used simultaneously. Secondly, using IS does have an effect on battery discharge rate but not enough to be a cause for concern in my experience. Batteries are so inexpensive why not buy two more batteries so you can keep two in the grip and two spare?

I agree. Just go to sterlingtek and get yourself two spares. Always good to have spares

As OP is in the UK, 7dayshop.com have batteries for the 400D at under £8 for two (plus P&P) - pretty good value if you ask me. I've been using 7dayshop batteries in my 5D and 400D for some time now without any problem.

I use a grip with the 2 batteries and never have a problem. I keep two extras on hand but never need them. I shoot all week long on 2 batteries. I shoot birds and I am constantly focusing and burning up the IS...no problems with batteries.

Thanks all, I can now move on