The Canon LP-E4 Battery Pack is the power source for the Canon EOS-1D Mark IV DSLR Canon EOS-1D Mark III DSLR and Canon EOS-1Ds Mark III DSLR. The LP-E4 is a rather small battery when compared to the prior 1-Series body's NiCAD power source as seen compared below.
The LP-E4 Li-ION battery delivers a huge number of frames (approaching 2,000) from a single charge. I always have a spare battery on hand, but with this many frames from a single charge, it is harder to justify having the extra battery.
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