So I just received the LanParte Li-ion Battery Packs a short while back. I was pretty curious to see what the run time was actually going to be like, so here's a video showing a continuous time lapse test with a Canon 5D Mark II. Specs state that the LanParte External Battery is equivalent to 4 LP-E6 batteries. The overall run time during this continuous shooting test ran for just over 5 hours.
The only problem was that my order did not come with was the proper plug for USA outlets, but we happened to have a converter on hand to charge up the pack. Or maybe you may already have a 12V 2A adapter with a 2.5/5.5 tip like this (found here). These battery packs are available in LP-E6 or LP-E8 battery adapters so it can power most Canon HD Video DSLRs (including all REBEL HDSLR cameras) out on the market today. You can find the LanParte External Battery for Canon Cameras via eBay (click here).
Lanparte Li-Ion External Battery Packs for Canon DSLR Cameras