The INA219 FeatherWing makes power-monitoring problems a thing of the past. Instead of struggling with two multimeters, you can just use the handy INA219B chip on this breakout to both measure both the high side voltage and DC current draw over I2C with 1% precision. Works with any Feather boards including the new Particle Argon, Boron, and Xenon.
This chip is smarter than your average current-measuring devices. It can handle high side current measuring, up to +26VDC, even though it is powered with 3.3V. It will also report back that high side voltage, which is great for tracking battery life or solar panels. Communicates over I2C and possible to change the I2C address to have up to 4 of these Wings on one Feather.