In addition to the obvious Battery FAQ, one that often gets ignored, for whatever lazy reasons, you can see, that you only have 90% percent of you capacity left, which might be due to lots of usage (357 cycles) or even improper usage (as described in the FAQ) or it might have to do with a process hogging down your CPU.
As you haven't reported what battery life you get (in minutes or even hours) and what usage you have and how that affects the CPU (which can be monitored via Activity Monitor), there can be plenty of reasons, but reading that FAQ should be a good start.