In general capacitors have much higher power density but much lower energy densities than batteries and supercapacitors are somewhere in between. http://large.

In general capacitors have much higher power density but much lower energy densities than batteries and supercapacitors are somewhere in between. http://large.stanford.edu/courses/2012/ph240/aslani1/ http://large.stanford.edu/courses/2012/ph240/aslani1/ Using a capacitor for the last 10% might make sense, or it might not. It's all about the specific numbers. It might be that a larger battery charged up to 90% might be better than a slightly smaller battery charged to 100% with the assistance of a capacitor. If you're adding a capacitor for power reasons anyways this might be a way to get more use out of it.