A Voltwatch installed in your plane does nearly as good a job of detecting servo stalling, push rod friction, poor switch etc. plus it is always there and you can check prior to and after each flight with no added equipment to have to find and plug in. If you see those LED's dance up and down the strip when you cycle the sticks, you know you have a problem. The nice thing about the Voltwatch, it checks much more than just the battery condition under a static load.