The eLogger V3 from Eagle Tree Systems is an in-flight data logger which continuously records volts, amps, watts, and milliamp-hours to enable pilots to analyze the performance of their electric power systems. In addition, it supports a wide variety of optional sensors to record altitude, airspeed, component temperatures, RPM, and more.

Specifications
Dimensions :2.25" x 1" x 0.5"
Weight :0.7 ounces (20 grams)
Voltage:5 to 70V
Amperage :Up to 100 amps
Temperature :0 to 424F
RPM: 100 to 50,000
Street Price :$70 for the eLogger, $40 for the PowerPanel, $15 for the brushless RPM sensor, $10 each for either temperature sensor, $30 for the altimeter

The eLogger is a small device which continuously records these values to its internal memory. Once back on the ground, these log files can be downloaded to a computer for graphing and analysis. The device can also be used to display live values for all of its sensors, which means it doubles as a wattmeter on the bench.