What Mike describes is what most guys do at my field too. This works well 99% of the time. However if you have one cell go bad in your pack after the first or second flight, you'd never know it. That's why I feel better with a voltage monitor. I've seen some of my older packs, that normally last 3-5 flights, drop off fast after one flight. Needless to say I chuck them in the garbage and get new ones.