My MacBook is my second computer, and I don't use it much, but I've been using it a lot in the past week. I'm getting perhaps 6 hours of battery life, without using a lot of apps. One thing I notice is that two processes, mtmd and mtmfs pop up frequently, using 100% or more of CPU (of a core) and do so for a while. When I check Activity Monitor, and look at Energy, the app listed as having the highest impact is Time Machine, way above Safari which is the second. These two processes are apparently related to Time Machine, and have something to do with creating local snapshots. But I'm only using the MacBook at my home office, so it's on the network where my Time Machine backup device is located.
It's worth noting that this probably didn't start until recently. While I didn't use the MacBook a lot, it's always on my desk, and I use it for screenshots and testing apps. I had never noticed any problems with the battery until recently. I'm speculating that an El Capitan update did something to the Time Machine processes.
I've contacted AppleCare, and spent a lot of time on this, sending them logs and other data, and I'm waiting to hear back.
