Seems like my trackpad is never sleeping/shutting off
I've had to track this down and have found that keeping a log has helped me identify which trackpads are going through batteries faster than the others.

Once a week, I'm recording what the OS thinks is the battery level. I've been able to catch bad rechargeable cells as well as one faulty trackpad (among lots) that seemed to be less power efficient. Showing the log to the genius bar was all they needed to offer a swap. 

If you don't have a lot of devices - it might be something you just throw good alkaline batteries at until you have a feeling if it's normal. I would go into the genius bar with the Mac and the trackpad to establish the idea you'll be testing it and ask if they have any insight.

Unless you have something capacative on the surface (or very near the surface), it shouldn't matter if your Mac is awake or asleep as the trackpad itself will go to sleep. You can also disable sleep / PowerNap and such once you are sure of the normal weekly drain on a battery and see if it makes any difference.

As to catching the culprit for wake issues - open the terminal and type pmset -g log to dump the history of sleeps, wakes and much more. The manual page for pmset will help if you need more detailed logs than that, but hopefully you can catch whatever event is causing the OS to wake up.