The generic NB-2LH replacement battery ($20) from my Canon EOS Rebel did not last nearly as long on a charge as the original equipment battery ($60).
I went online to find if there were reviews of 3rd party batteries. I couldn't find much.

What I found was many people use 3rd party batteries with no problems.
Others report:
- Shorter use time
  Higher miliamper Hour (mAh) ratings do not necessarily correspond to more life on a charge.
- Bad performance in cold weather
- Inability to communicate with software in newer cameras or upgraded firmware.

The current "smart" Lithium-ion batteries have an IC circuit inside which allows the camera to read the charge level, and compute the number of shots remaining.
Some generics do not have this.
One person reported some third-party Nikon EN-EL3e battery clones can only work with the D200 but not the D300.

You can save significantly with a generic.
An OEM Canon NB-2LH costs $64 at amazon.
You can get 2 UpStart NB-2LH replacements for $16 at amazon.

The original NB-2LH is 720mAh. You can get replacements with up to 1,900mAh.

There are so many types I couldn't find any good reviews.

There were lots of comments in the forums like "You spend $X,XXX on other equipment, why skimp on batteries?"

Several people reported satisfactory results with Watson batteries sold at B&H and Amazon.
At Canon vs Third Party Battery Test, Dave Dugdale, who does video courses on photography, reports on testing a brand new Watson LP-E6N (2,000mAh) ($40 vs $62 ) which lasted 1:09 in field monitor and a Canon LP-E6 (1,800mAh) which lasted 1:28. The Watson did communicate with his 5D Mark 3. One person said " I recommend you use Watson battery for few weeks, recharge it few times. Then test the performance again. You have to know, that batteries with right handling get longer and longer performance."

LP-E6 replacement ratings xx (nnn) - xx - Score out of 5, nnn - number of customer reviews
        Amazon                      B&H
Canon LP-E6 1800mAh 4.5 (773) $67 4.8 (2,609) $62
Canon LP-E6N 1865mAh 4.6 (54) $64 4.8 (93)    $62 *
Watson LP-6E 1750mAh 4.2 (17) $35 
Watson LP-E6N 2000mAh         $43 4.5 (69)    $40
Wasabi 2600mAh  4.3 (1,415) 2 + charger for $30 
STK 2600mAh     4.4 (1,011)     $14
BM  2600mAh     4.4 (288) 2 for $28
Vivitar 2000mAH  4.4 (147) 2 for $22
* Note that the LP-E6 and LP-E6N can be used interchangeably, but the LP-E6 cannot be charged in the E6N charger. The battery differences are due to changed battery design regulations in Japan.

TheTechReviewer has had good luck with Wasabi and Watson. Others also recommended Wasabi.

Cheap Camera Batteries & Chargers for Sale at Dealextreme - DX

See notes in Home and Garden

Airline regulations on lithium batteries:
You may not pack a spare lithium battery in your checked baggage. You may bring spare lithium batteries with you in carry-on baggage. Even though we recommend carrying your devices with you in carry-on baggage as well, if you must bring one in checked baggage, you may check it with the batteries installed." Links:
About batteries in the Home and Garden section
replacement Canon camera battery guide |
third party - Should I buy an original manufacturer battery, or is a generic brand OK? - Photography Stack Exchange
third party - Should I buy an original manufacturer battery, or is a generic brand OK? - Photography Stack Exchange
Top 5 Best Third Party Camera Batteries |

last updated 25 June 2015