This may be old news to some, but if you own a digital multimeter it comes in handy for testing the drain on your batteries under flight loads to see if they are up to the task. Just make a lead for your meter to plug into a servo extension, which will give you the actual voltage your receiver is getting. Here are the checks you can do with the tool.
1. Check every control surface through its full movement to see if it's binding. Do this one regularly to find faulty servos or wiring.
2. Manually stall one or more servos to see how much voltage you get under maximum flight load.
3. Cycle after test two fails to see how much useable capacity you have.

Since the stall test is repeatable, it is just as good as using a loaded ESV. This tester also tells you if you are using good enough batteries for your application. If the voltage falls too low but your cycler says you still have say 2/3 capacity in your batteries, then you are putting too much draw on your batteries. Switching to a higher discharge rating or higher capacity will give you better battery life and many more flights per charge. The multimeter also comes in handy for checking the impedance of wire connections and solder joints, and can check the current draw of servos to spot potential problems before they cost your an airplane.