IF you want to be sure...
It is quite simple,
Canon branded battery's are designed to communicate with the camera so you know how much battery life you have to start and when it's time to get your spare ready by the camera's battery indicator.
Off brand replacement (cheeper) batteries will power the camera but do not allow the camera to monitor the batteries life or let you know the usage by the camera's battery indicator.
When I bought my 7D I wasn't sold on why I should have to but a Canon branded battery at a much higher price than the off-brand battery. I found the off brand battery to be useful as a backup battery and not reliable nor did the off brand give me the range of battery life that the Canon branded batteries do.
If you only need a safety net backup for the casual shooter they are fine but I had to purchase a second Canon battery for the long shooting life, communication with the camera and the camera's monitoring of Canon branded batteries.
If you are like me and wish to know the longevity of your battery then go with Canon's battery.
Great Battery for my 7D
I use this in my 7D not a 5D II.I like the way the battery looks with Canon Inscribed on it,which means,to me,that they take pride in their work and product.I have a Canon EOS Digital Rebel Xt,40D,50D and 1Ds Mark III, as well as the 7D.If they had used the same battery from any of these,it wouldn't have saved me money since I bought the BG-E7.I use the leveler,shooting info,and playback quite a bit on the rear LCD and I'm sure I'll start using the video mode more often.The battery seems to last about a day and a half without flash.I haven't done much flash photography.I have heard that you can shoot 600 pics and only use 2 bars.Hope this helps.
Well, it's a battery...
It's a battery, and it works. When I purcahsed my 5Dii I bought the grip and extra battery as a "base configuration" for my uses.
I'm thinking they are marketed with conservative numbers as they say only 850 shots per charge (and only 800 for the BP511-a). With two batteries in a grip, I made it through 2500 shots two weekends running. So I'm far exceeding the specs listed on the page.
I have purcahsed "off-brands" in the past, but I'm not keen on the fact that you loose certain capabilities with the 5Dii (in terms of battery info). I guess that was a good move by Canon to make peope shy away from aftermarket batteries.
Canon battery for 7D
Canon batteries are outstanding in durability and reliability. I use a 40D and a 7D and they are both excellent batteries. It is difficult to compare them directly since I use the 7D in video mode a lot and the 40D has no video mode. They seem to charge at about the same rate which is around a couple hours. I would like to see the 7D battery charge within an hour so I could get by with two batteries. I now carry three with me all the time to be sure one will be fully charged when I need it. I know the charge time is not unreasonable, but I need something to grump about.
The only problem I had with the 1st gen 5D was battery performance in cold weather. I made the switch to the Mark II in December and besides the great technology in the camera, the battery is a hidden gem. Recently I was on a shoot with a group and a 5D shooter had to switch to a point and shoot because the 5D battery lost all of it's juice in the cold weather. The Mark II's battery was still fully charged!!! I can honestly say, with my 5D, I always carried 2 batteries, with the Mark II, I only carry one and never came close to exhausting the battery during the day.
Maybe pricey, but I trust it in my Camer
I still buy third party BP-511 batteries for my 40D. For some reason I felt less inclined to search for a third party version of the LP-E6.
Third party BP-511 batteries were cheaper (often 50% or more) but one of them dropped its charging capability quickly. So I decided it might be worth getting a Canon brand LP-E6.
Yes, I wish it were cheaper but I feel less of a need to have a lot of them since they can report their condition, so I know in advance if they're ready to go or not.
Worth buying Canon
I've used the no-name brands and they just don't work as well. Some hold a charge but fail after a year or two. Some don't interact with the 5D Mark II's battery indicator (they will power the camera but give no indication of how much charge is left). I finally decided to just get the canon battery and it's been great. Worth paying a little extra for that reliability.
I have two of these batteries for my Canon 5D Mark III. One came with the camera, one purchased separate. They both take the same amount of time to charge and to discharge. I shoot in RAW. I haven't actually calculated the number of hours I get out of a battery, but I did 3 shoots on one battery. One being a 3 hour newborn shoot.
Canon Battery Pack LP-E6
I number my batteries to be sure & rotate them through the camera & always run them down to 20% power as close as I can to be sure & charge from "bottom" up. Works of course with camera battery menu. As usual, Canon quality is present...but price always makes me gasp. Wished more camera bodies used same battery model or flashes.
Go for Quality !!
I use this with my Canon 7D. It's such an important component to my camera that I couldn't bring myself to buy a 3rd party. It's a piece of mind that my equipment will work together without any conflicts. It has a quick charge, long lasting and very reliable!!
You get what you pay for!!