I took a while to reverse engineer Canon batteries. LC-E6 is expensive and sometimes hard to find in stores. The Series 7 SL-E6 is a 7.4v, 1800mAh Lithium Ion battery pack which can charge on the Canon LC-E6. The SL-E6 battery also communicates with the EOS 5D Mark II and 7D digital cameras, allowing you to check the remaining capacity on the camera's power source info screen. The SL-E6 does not have the data chip necessary to provide storeable information on the Canon 5D/7D's battery registry screen.
[caption id="attachment_646" align="alignnone" width="300" caption="SL-E6"][/caption]
It is available on Amazon from $56.49.