Now you've got it. And, no I didn't take the grip apart for a 10D, 20D/30D, or 5D. But my XT grip is different, in that the battery holder slides out from the side, so the jumpers between the two batteries are easy to see. It would be a simple matter to check the wiring of a 30D or 5D grip with an ohmmeter, and no disassembly would be required. Think Occam's Razor. Why extra curcuitry to switch between two batteries, if none is required?
i had always thought that using different rated batteries are not a good idea. I have read that using different rated batteries (and even different kinds) in, say a flash, can cause problems. Maybe that is the exception to this. I always use two Canon 511's in my grip. I have yet to exhaust the batteries.
HBOC: Please see page 1 of this thread for a rather comprehensive explanation of when to mix and when not to mix batteries having different ratings.
dcains: It was access-wise not exactly simple to measure the 5D grip wiring with ohmmeter, but it was possible. The result was that minus poles are jumper-wired, but plus poles are not: my DMM showed about 8 Mohms & 16 Mohms resistanc between them, depending on which polarity I used when measuring. Reading was not fully stable, but there was some capacitance which was slowly charged by the measurement current.
The measurement result points to some kind of electronic circuitry, and there is good rationale for it: Batteries, especially lithium-ion batteries, may not be short-circuited. If one battery happens to fail badly, it can start to resemble a short circuit, and if you jumper-wire another battery to it, the good one might explode, even if it is not made by Sony ... Even if both batteries are OK, the instant equalisation of their output voltages is not by any means power efficient nor healthy to the batteries, because of the high currents involved.
I really don't know why and how an XT grip can jumper-wire the batteries, unless the XT batteries themselves contain a current limiting mechanism (a resistor in simpliest case) to make them short-circuit proof.
Well, I guess you're correct about the 5D grip, since you've made the measurments, and perhaps you're also correct in that there is a protection circuit in place.
I just pulled the bottom trim panel off the battery tary in my XT grip, and I was correct - nothing but jumpers. There is no circuitry of any sort in the XT grip, and the pair of batteries are simply wired in parallel. Interesting that they'd be so different from one another.
