An expanded scale voltmeter is useless for anything except as a confidence booster. All it can tell you, with accuracy, is if the pack is already discharged and unsafe to use.

It's use is as effective as determining the VOLUME of air in a wheel by reading the tire pressure. Logic will tell you that this can't be done. Consider a small trailer wheel and a semi wheel. Inflate both to 40psi - which one contains the most air? The ESV's don't allow for diferent capacity packs, only cell count - go figure. NiCads and NiMH voltage curves are so flat when not in a discharged state that voltage reading indicates NOTHING of the remaining capacity.

The safest way is to discharge the remaining capacity after use and deducting it from the actual capacity. Divide the used capacity by the number of flights and you will know how much capacity is used, on average, during each flight. This way you can determine how many safe flights can be made with a pack. A good cut-off point is at least 30% before the capacity will be used up. (Ie, only use 70% of the capacity.) Remember that averages during flights will vary.

The fire and forget method of wall-wart chargers and guesswork, will eventually cause free-flight - not fun at all.

Safe Flying!