Everyone Needs One
You've gotta have one of these. It will pay for itself in a month on saved batteries. Have already used it to catch "brand new" batteries straight out of a new package that were actually at 80% and would have failed in my wireless during the show. I check every battery on our stage with it before shows now- wireless, pedals, etc. The peace of mind is invaluable. If you use batteries, you need this. And its really pretty cheap for what it does for you.