I need to measure the energy usage of a small bluetooth device which is normally operated by a coin cell 3v battery.
Background: Using an oscilloscope I was able to get fairly good pictures of the energy used during standard connection and advertising events (measuring current through and external 10ohm resistor and integrating), but that is in a steady state condition when not much is going on and the event is easily captured with oscilloscope. More complex interactions happen between the device and the other bluetooth device it is connected to (typically a smart phone) during re-connection events and when characteristics are being read or written.
Questions: Is it possible to use a simple capacitor to measure energy usage by charging the capacitor initially, then running the device off the capacitor power for a few minutes during the test and then measuring the remaining charge? How accurate would that be?
What other techniques would you recommend?
(edit: note I'm actually interested in mAH usage not energy since ultimately the goal is to estimate battery life and battery is rated for 220mAH)