Battery indicator "jumps" from high to low percentage

A

AC Question

Hi there,
my Motorola Droid 4 behaves in a strange way. From a couple of weeks the battery indicator suddenly drops, for example from to 44% to 18%, from 60% to 40%, and so on.

Can anyone explain me why, and how to fix the problem? It's kind of annoying relying to your phone and then realizing it won't work for long.

Thank you so much,
Elisa