Sleeve with 4 x Procell AA Batteries
For wireless microphones, and really anything that requires serious staying power from 1.5v AA battery, let ProCell be your first choice.
Broadcasters, Stage Managers and Theatres all around the world depend on the battery that gives them maximum output for as long (and consistently) as possible.
Grab as many sleeves as you need. They work out cheaper than your local supermarket. Also get some for your kid's toys, remote controls and other gadgets...