Overview
Many current measuring devices are only good for low side measuring and monitoring.  This means that unless you want to get a battery involved, you have to place the measurement resistor between the target ground and true ground.  Doing 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 breakout board from Adafruit is much smarter - it can handle high side current measuring, up to +26 VDC, even though it is powered by 3.3 or 5 V.  It will also report back the high side voltage, which is good fro tracking battery life or solar panel output.

A precision amplifier measures the voltage across the 0.1 ohm, 1% sense resistor.  Since the amplifier maximum input difference is +-320mV this means that it can measure up to +-3.2 Amps.  With the internal 12-bit ADC, the resolution at +-3.2 A range is 0.8 mA.  If you were to set the internal gain to the minimum of div8, the max current would be +-400mA and the resolution would be 0.1 mA.  Advanced users can remove the 0.1. ohm current sense resistor and replace it with their own to change the range, for example a 0.01 ohm resistor to measure up to 32 Amps with a resolution of 8mA.

Key Features:
  - High-side voltage measuring enables battery and solar panel monitoring  
  - Wide operating voltage while protecting your microcontroller and communicating at a 3.3 or 5 V level 
  - Swappable current sensing resistor allows custom current sensing values

Application Ideas:
  - Solar Panel Output Monitoring
  - Project Battery Life Monitor
  - Power Management

Details
  - 0.1 ohm 1% 2 W current sense resistor
  - Up to +26 V target voltage
  - Up to +-3.2 A current measurement, with +-0.8 mA resolution
  - Voltage requirements: 3 to 5 V
  - Current requirements: 1 mA
  - Communication: I2C
  - Dimensions: 0.9 x 0.8 in (2.29 x 2.03 cm) PCB
  - Operating temp range: -40 to +257 °F (-40 to +125 °C)