I use Duracell ProCells because they're excellent batteries and you know for sure if they've been used or not (9v cap). I also like the ProCells because you can order them in bulk and they're accepted everywhere as the industry standard. In fact, they're pretty much the industry standard for any professional industry. Heck even my mom uses them at the hospital, it's the only battery they use. It's a waste of money to buy batteries through retail. The caps on the 9volts are really helpful for when you're dealing with a new crew and you want to keep
track of battery usage (no more mixing up fresh batteries). Who wants
meter hundreds of batteries just because someone didn't do their job? They seem to hold charge more consistently battery to battery then standard grade batteries. In fact, I never have to order no batteries for regular school and outside events. There are always batteries left over with plenty of charge from our shows. So, they get quite a
bit of re-use. But we don't have a huge overstock of used batteries, there is a nice balance between what's coming in fresh and what's going out dead. We always have a little
bit more coming in then what's coming out, but sometimes we need to use a large quantity of batteries for lavs and multiple speakers for informal events
For every formal theater production w/lavs, I order the quantity needed multiplied by every performance and formal dress rehersal. Then I'll get an additional amount for regular rehersals where redundency isn't so critical. If a battery goes out, the lav tech can just swap batteries when an actor isn't on. Or sometimes, if it's not uncalled for, the tech can just change right on
stage in the middle of a rehersal. The
point of running wireless during those rehersals is to see if the design is being executed properly, getting a feel for the cues/mixing the show, and seeing what isn't working out. So it's not the end of the world if you reuse a battery and a lav goes out once and while, all you have to do is just change the battery.