Suffers from the same basic problem of gasoline vs. electric cars - a kilogram of a chemical fuel (gasoline, nitrocellulose) has *way* more energy than a kilogram of battery (on the order of one hundred times more). So 50 grains of powder (about 3 grams) carries about about the same amount of energy as 300 grams of a high performance battery. So your battery pack would weigh half a pound or so for each shot's worth of stored energy.
(Whoever figures out how to make batteries about ten times more energy-dense than they are today, will get very rich....)
There still is a certain elegance to burning chemicals, eh...?