I don't think it matters very much which one you get. Either way it will only provide power to the monitor, will not be interchangeable with the battery in your camera, and will need it's own charger.
The BP511/511A is "older tech". It was used in many Canon cameras up through 50D. They are still widely available and usually less expensive.
The LP-E6 is a larger version than the LP-E8 your camera uses. Canon 60D, 7D, 5DII, 70D, 5DIII and 6D all use the LP-E6. The Rebel series cameras usch as yours use the smaller LP-E8.
The LP-E6 is more expensive than BP511/511A, but I'd guess LP-E6 will have about 40 or 50% longer running time too. I get about 40 or 50% more shots with my cameras using LP-E6, than I did with cameras using BP511/511A. I used to carry two backup batteries for every BP511.... With LP-E6, I only carry one backup per, thanks to the extra run time I see with them.
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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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