The INA219B breakout board and the INA219 FeatherWing will solve all your power-monitoring problems. Instead of struggling with two multimeters, you can use this breakout to measure both the high side voltage and DC current draw over I2C with 1% precision.
As if that weren't enough, we've now also added SparkFun qwiic compatible STEMMA QT connectors for the I2C bus so you don't even need to solder the I2C and power lines. Just wire up to your favorite micro using a STEMMA QT adapter cable. The Stemma QT connectors also mean the INA219 can be used with our various associated accessories. QT Cable is not included, but we have a variety in the shop.
Most current-measuring devices such as our current panel meter are only good for low side measuring. That means that unless you want to get a battery involved, you have to stick the measurement resistor between the target ground and true ground.
Since the voltage drop across the resistor is proportional to the current draw, this means that the ground reference will change with varying current. Having a shifting ground reference can cause problems for many circuits.
The INA219B chip is much smarter - it can handle high side current measuring, up to +26VDC, even though it is powered with 3 or 5V. It will also report back that high side voltage, which is great for tracking battery life or solar panels.