RE: "Tower Pro" "Volt Watch"
Tower's [Hobbico] voltmeter has served me well. It evaluates 6 and 4.8 volt packs with a dummy load. I don't fly anything that matters if the loaded reading [for a 4 cell pack] is below 5 volts....because I typically use 300-350 mill packs. NIMH packs are a nice improvement over NICAD, but you have to watch them like a hawk.