If your MacBook (any model) is not charging to 100%, it may need to be recalibrated. Apple explains how to do this, but basically it comes down to three steps:
Fully charge your MacBook (and leave it charged for about 2 hours)
Fully drain your MacBook (by using it on battery until it turns off)
Fully recharge your MacBook again.
That should help the battery indicator recalibrate so that it shows the correct information. If it doesn't, you might need to reset the System Management Controller (SMC), but in most case I've found that a simple recalibration will work.
When I recalibrate, I prefer to make sure that my MacBook will not be interrupted at all either during th
