"I had a friend with a 7D that bought a cheap 3rd world import battery that swelled up inside the camera and could not be removed. The camera had to go in for service, some cheap battery, right? Swelling is just before exploding."
Again, I am not recommending and personally don't use 3rd party LP-E6, which are the battery type 7D uses. I only use OEM Canon LP-E6 LIon batts in my later model cameras. Early on when they were first introduced a lot of 3rd party LP-E6 seemed to be repackaged NiCads, some even came with warnings not to use the Canon charger. Things have improved, but I'm not sure to what degree and I still don't entirely trust them. In addition, the OEM LP-E6 (and similar LP-E8, etc.) include other circuitry to communicate with the camera (and possibly the charger). I've seen enough reports about that not working properly to stick with the Canon OEM LP-E6s in my 5DII and 7Ds. Also, the extra cost is mitigated a bit because the LP-E6 give so many more shots than BP511/511A did.... I only carry one set of LP-E6 backups per camera now, where I used to have to carry two sets per camera to get through a long day's shoot, when using BP511/511A.
However the OP was asking about BP511 for use in a BP-E2 (or E2N) on a 20D. Those are simple NiCads and in my experience the 3rd party generic batts are fine. I have at least a dozen that have served well for a five or more years, alongside a similar number of OEM Canon.
"I've got some 3rd party ones which in my opinion were made with very low cost ingredients (they run down quickly & didn't last many recharge cycles when compared to my Canon brand ones"
My experience with the 3rd party BP511s was just the opposite. They tended to last at least as long, maybe even longer and give more shots than some of my original Canon BP511. The 3rd party are rated a bit higher capacity than the original BP511s, are closer to "upgraded" BP511A.
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Alan Myers
San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7D(x2), 50D(x3), some other cameras, various lenses & accessories
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