This breakout board will solve all your power-monitoring problems.
Instead of struggling with two multimeters, you can just use the handy
INA219 chip on this breakout to both measure both the high side voltage
and DC current draw over I2C with 1% precision.
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. This can cause problems with circuits since electronics
tend to not like it when the ground references change and move with
varying current draw. This 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.
A precision amplifier
measures the voltage across the 0.1 ohm, 1% sense resistor. Since the
amplifier maximum input difference is ±320mV this means it can measure
up to ±3.2 Amps. With the internal 12 bit ADC, the resolution at ±3.2A
range is 0.8mA. With the internal gain set at the minimum of div8, the
max current is ±400mA and the resolution is 0.1mA. Advanced hackers can
remove the 0.1 ohm current sense resistor and replace it with their own
to change the range (say a 0.01 ohm to measure up 32 Amps with a
resolution of 8mA)