Battery grip battery usage...

Does anyone know how the camera uses a pair of batteries when in a battery grip? Do they drain equally or does the camera run through one of them and then jump to the next? I ask because the other day while out shooting, when I checked the battery life, it told me at one point that both batteries were at approximately 15%. When i got home, i took one battery out and it still read 15%, then I switched that battery out for the other one, it said it was at 94%. I'm confused. Anyone got any thoughts on this? Thanks.

From what I understand it tries to equal them out, at least on my 7D. Usually I charge both at the same time but the few times I haven't it used the battery with the higher charge.

It will drain them equally. The reason you get the same percentage whether it's with one or two batteries is because one is 15% out of 100% and two are 30% out of 200%, which is of course also 15% of 100%. Now this is all assuming you start off with two fully charged batteries, if you swap out one for another at 100% I assume it would give you a 58% total, and once the 15% battery is drained it would then carry on to run off just the one battery.

I had thought it drained them equally, but for some odd reason the last few times I've pulled mine out of the grip to charge them, one of them was always showing fully charged.

Are you using the official Canon grip? I always thought it used them equally just like the third party ones, however I only have the Meike grip and its instructions to check so may be mistaken.

That is weird, everything I've read about it is that it uses them simultaneously.

The Ran wrote in post #13094294
Are you using the official Canon grip? I always thought it used them equally just like the third party ones, however I only have the Meike grip and its instructions to check so may be mistaken.

All Canon, all the time...batteries too

My Phottix grips on my 20D and 50D use the power out of the left hand (looking from the back) first and when drained automatically use the right hand battery.

yogestee wrote in post #13095837
My Phottix grips on my 20D and 50D use the power out of the left hand (looking from the back) first and when drained automatically use the right hand battery.

Seems that is what my Opteka grip is doing as well.

Long time ago I read an explanation by Canon's Chuck Westfall IRRC, about battery usage in Canon grips.
If voltage in two batteries is not equal, grip discharges battery with higher voltage first.
When voltages on both batteries become equal, discharging goes alternatively, one at the time.

I don't remember any more details, perhaps someone has more reliable source..
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Okay, here is one from the Similar Threads:

https://photography-on-the.net …hp?p=9281279&po​stcount=88

yogestee wrote in post #13095837
My Phottix grips on my 20D and 50D use the power out of the left hand (looking from the back) first and when drained automatically use the right hand battery.

Both my 5D and 20D grips (Canon) do this. With batteries bought at the same time and never mixed or swapped over between grips. Always drains LH battery first; the RH goes to the charger and full charge pops up in 30 seconds. I swap over the batteries in the grip after charge to equalise usage.