That’s a question I get asked at the field most often with a voltage reading. Usually I’ll kinda cringe and say yes most likely. If I get a sense of the flyer needing more info, I give them the following spiel.
Ideally, for a nicad and nimh pack we should be keeping track of the energy taken out. Voltage can give us a rough indication, and is acutually an indirect reading of the energy, not the best method. Not the best because the dropoff at the limit is so dramatic. Look for discharge curves on the net. In that equipment that is small enough and economically makes sense is still not around, here is what I do.
For a new pack I’ll usually put is through a couple of charge and discharge cycles, just to see if it is relatively heathly or not. Equipment is nothing fancy, in fact I use an 30 year old ACE one with auto cutoff. Personally I think auto cutoff on discharge is a must since I know I’d miss it manually. I then install the pack in the plane and charge it normally the night before with the wall wart. At the field, I keep track mentally of the number and lenght of flights made, then I go home and put it on the discharger. I do this for several flying sessions and this gives me a rough idea of how many flights I can put on. Additionally, I’l do this at least once a year to gauge the packs health.
Similarly, for the transmitter, I’ll give it a full charge, then run and time the thing until the low voltage alarm goes off. This assumes one has a computer radio, use a cycler on the pack itself for simpler radios. If I don’t get enough power for an hour or two or whatever the particular pack should give me, I know the battery is off. Additionally, from time to time I see if I can get at least 3 to 5 minutes in this “alarm zone” to simulate this happening during a flight.