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 p.1 #7 · Mixing 3rd Party Batteries | |
Tentacle wrote:
No, in a Canon grip the batteries are used parallel, not serial. (The Nikon grip apparently uses one after the other.) At least, my 10D with grip will draw from both BP511s simultaneously. I find that, once it's recharging time, both cells have the same amount of charge left in them.
[edit] Hmmm, after re-reading the above, maybe I'm wrong here...
Well, Nikon camera grip (at least D200) uses first one battery, and then it starts using the next one. This makes it possible to remove the already empty one and charge it while using your camera with 1 (or 2, if you have a 3rd battery) fully charged batteries. Canon camera grips use some method (probably the alternating one as described by Lance on this page), which results having both batteries half-empty (and later on empty) simultaneously. The Nikon way seems to be more practical for the user. 
But it is obvious that batteries in both Nikon and Canon camera grips are used electrically similarly, i.e. just one battery is in active use at each moment:
1. They can't work in series connection, because that would double the operating voltage and thus require extra electronics, which would cause extra power losses and unmotivated production cost increase.
2. They can't work actively in parallel connection, because that would require additional electronics (and power losses and extra cost) to balance between the always-existing, even minor cell voltage & impedance differences between the two batteries, even if they are from same manufacturer's same production lot and have identical charge/discharge history.
Anyone knows what the manual says on this?
In general, it's still not wise to use batteries with different capacities. It's best to keep rechargable batteries in fixed identical pairs, which even means you should avoid mixing used and new batteries of the same type/model because capacity will slip some over time. Same goes for the 4 AA sets that go into a Speedlite.
The advice above is not valid for the camera grip lithium battery packs, since they are used independent of each other, as explained above.
Instead, this advice is very valid for sets of any amount of AA batteries which are used simultaneously in series connection, like AA batteries in the AA battery holder of camera grip, in flash unit, in external battery power pack of flash, etc. The reason for this is very simple: In series connection, what you get out of the AA battery set, is the sum of output voltages divided by the sum of internal impedances of each single AA battery, and if you have any individual battery which is weaker than the others (in either respect), it unnecessary limits the performance of the whole set.
Does this sound convincing enough? 
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