I've always felt that shopping for camera batteries is about as exciting as buying tires for a station wagon. Yes, you need them both, but they cost more than you want to spend and are less than thrilling to use.
Since the manufacturer's batteries are pricy, it's tempting to save a few bucks using batteries made by other folks. So I decided to put this to the test with my Canon PowerShot S90
The specs for both batteries are the same. And after a few months of alternating back and forth between the two, I haven't noticed any performance differences.
So my initial conclusion is: as long as the third party battery is of good quality, I don't see a reason to pay more for the manufacturer's brand. If you've tested this with other cameras, please post a comment with your findings.
A few months might not be long enough to tell. I just retired a digital camera after six years. The original Konica-Minolta battery was still working. I've had to throw out several non K-M batteries. I usually tried to have three batteries on hand as the camera would go through more than one battery on a busy day.
But your "as long as the third party battery is of good quality" is probably correct. It's just figuring out that magic "good quality."
Have used third party batteries for Canon G2 and G9 for thre years with no problems.
I have third-party batteries for my 7D. And while they were cheap, they don't provide the battery level to the body, so I have to always guess if I can get a series of shots. If I really care, I swap my original battery back for a series, then go back to the third-party battery. It also requires a different charger, so I have to pack two chargers instead of one. If I had to do it over again, I'm not sure I'd have bought them.
I agree with Fred. Your disclaimer about "good quality" is quite a loophole. There is no practical method to judge the quality of a third party battery without actually having one to try or having a web review like yours.
I think you can make a reasonable evaluation of a third party battery. There are a lot of good brands out there, such as Promaster, that provide good product for less money. But just like with everything else, please go with what you're most comfortable with.
But heres the rub- if the third party damages your camera......your warranty is void. I had a D200 that simply shut down on me. When I brought it in to Nikon- they blamed the battery and told me I would have to pay for the repair, despite the camera being under warranty. I may have saved 20 bucks at the start- but paying 175 for the repair is a great example of pennny wise- pound foolish!
I have used 3rd party BP 511 compatible batteries with my 20D without any problem, since 2004. Same with third-parties for the Canon ELPH.
LP-E6 like in the 7D and 5DMkII, I'm not sure. I have be hesitant to get third a party one as most of the time they come with their own charger... (huh?) because they don't work with Canon's.
Smart battery vs dumb battery. Randal experience with the 7D is what will happen with "smart" batteries (like in the 5DMkII).
And the price difference is quite severe. Even more that one seem to be able to get the Canon one for 40$ less in the US than Canada. (ie it is even cheaper for us to get third parties)
I used both name brand and 3rd party batteries in my cameras and have found that in general, the 3rd party ones die more quickly (i.e., won't hold a charge). But the lower price may be worth it. Also, battery life is very dependent on how old the battery is when you buy it: if it's already a year old when you buy it from the discounter, that's 1/3 of the battery's life gone.