Longshadow: I believe your are very correct. In my case, I do teach electronics in my physics class. When two identical batteries are connected in -parallel-, the current is doubled, and the voltage stays constant. That is why we get a "longer life" before we need to recharge them, both of them. Like you, I have Canon, and always with a battery grips. I will always remember the bitter cold winter storm we had a few years ago. I went to a local park to capture many beautiful images. Two fresh batters in the grip, and I put two more in a shirt pocket that would keep them close to my chest, hence receive body heat from me. Remember, in nearly all batteries, the output is a function of temperature. That's why in very cold weather, as the temp goes down, your "car battery cranking power" also goes down. So, back to the cold park. After about 40 minutes of shooting, the two in the pack ran down, so back to the car, and insert the two from my shirt pocket. Yep, I got another 40 minutes. In fact, I capture an image of a young father and his young child on a sled coming down a small hill, surrendered with snow covered pine trees on both sides. I capture some nice image. The dad asked if he could see them, and fell in love with the images. I told him to pick the one he likes best, and I'll email a .jpg to him. He told me used it to make their Christmas cards, all 400 of them. Kind of makes you feel good when you can 'make a difference'.

So, two (identical) batteries, in parallel, will double the current, and keep the voltage constant. In fact, I have a former student who likes to help fellow students when the bitter cold makes their cars difficult/impossible to start after classes. Dan bought a second truck batter, wired them in parallel and was then able to help many many students. 12vdc and a major high value of dc current. I hope this helps.

Sorry for the story about the young dad and child, but I thought the double battery part of the story might interest you and suggest we all look for ways to help other people with our images.
Bill

Canon cameras either...

- draw power from both batteries simultaneously (older models).

- draw power first from one battery, then when the power level runs low in that 1st battery, begins using the 2nd (newer models).

In the second example it's possible that only one of the batteries will need recharging. In the first example both will need recharging.

I don't think it's a hard and fast rule that the older models use the 1st method and the newer models use the 2nd. However, older cameras use "BP" type batteries, while newer Canon use "LP" series. A couple common examples of the older batteries are the BP511 and BP512. Some examples of the newer are LP-E6, LP-E12, LPE17. Both types are Lithioum-ion. The newer LP type have more tech in the battery that's primarily used to communicate with the camera. This communication may be why the newer grips use the batteries in the second method described above.

Some cameras might give you option to have the camera use either method. But that's not been the case with any Canon I've used with battery grips, which has probably been 8 or 10 different models over the years.