Although many on this thread seem to have an almost religious fervor on the subject of the Voltwatch, I don’t think it’s worth any more than a warm bucket of spit. It is completely uncalibrated, nor does it have a realistic load applied to the battery. You might as well look at moss growing on the north side of a tree to get an idea of the condition of your flight pack.

You are much better taking actual data (voltage measured by a digital voltmeter to at least 0.01 Volts) with a fixed load (just a simple power resistor), based on the size of the model, type of servos, and battery pack size. On top of making these spot measurements at the field before every flight, you need to test the pack from a fully charged state to its discharged state. Unlike so many posts on RCU where the poster states the battery is used up at 1.2 volts per cell, they actually continue to do useful work all the way down to 1.07 volts per cell. That is the typical voltage of the knee that has been mentioned. But since you can not depend on the cells to be completely balanced in capacity, it is a good idea to never go past the 1.12 V – 1.15V or about 4.5 to 4.6 Volts for a 4.8 Volt pack.

To find out how many flights a pack is good for, test the pack under your load and plot the voltage vs. time to below 4.40 volts. Charge up and go fly what you consider a safe number of flights. When you return home, continue to discharge the pack with your load resistor to see how much time is left to the 4.40 volts. This will tell you if you are safe or on the edge. Most of you will be surprised to find out that the pack has several more safe flights left in it and another one or two on the edge. Since you have already taken the data with the load resistor, you can always determine where you are in the battery pack’s discharged cycle, based on your discharge plot.

The other thing about the Voltwatch. It’s always discharging your battery while in flight. The specifications indicate that it could be using as much as 34 mA, which is a considerable discharge and wasted battery capacity.

But this is just my opinion, based on 37+ years of flying RC and a degree in Electrical Engineering.