Macbook Pro odd battery symbol meaning

Lately I've been seeing this symbol of a black battery icon with a black lightning bolt in it on my macbook pro 13" mid 2012 running Yosemite, When I see this symbol my magsafe light also isn't lit up. Usually just jiggling the magsafe while it's in the port does the trick and then my computer will start charging. My question is what does this symbol even mean and Is it something I need to be concerned about?