campgems, in your last paragraph, you mention putting a reasistor in the positive line form the volt meter . I have been using just that system for years. Wire in a 10 W 10 ohm resistor, in the positive line and have a plug fitted on the end to suit your charging plug in the model. This will place a load equivalent to 4 standard servos all working at once, and will give an accurate reading of the battery under load. Tandy's or any electrical supplies store will supply the resistor .
Bill