Here are a couple of possible solutions. Don’t know which one to recommend. Any idea how long a set of AAs last? That might give an idea of power consumption. Or maybe someone else knows.

I don’t have any experience with this company, yet anyway. Just always thought they have some interesting stuff.

http://dimensionengineering.com/DE-SWADJ.htm

http://dimensionengineering.com/DE-SWADJ3.htm