I'm using an APM2.6 board, and a 3DR voltage/current sensor board. I had to adjust the voltage multiplier upwards in order to get the voltage readings correct
If a 4-cell LiPO has measured internal resistances of 4,4,7,6 milliohms (respectively), that is a total of 21 milliohms. If I am drawing 30A (for example), that would mean the internal resistance of the batteries is dropping 30 X .021 = 630 millivolts. So, under that kind of load (typical for me) then my battery voltage reading will be .630 V too low. That is, when my battery has an actual voltage of 14V, I will measure only 13.37V. This is significant, since it amounts to 0.158 V/cell error. A fixed offset won't work, since the error depends on the exact current draw.
Does anyone build a voltage/current monitor that does this adjustment automatically? If not, is there a need for such a device (hint: I'm a hardware engineer).
Also, Mission Planner tells me the battery remaining and gives me verbal warnings. Where does the 'trigger' for those warnings originate - in the APM itself? In Mission Planner? If it is in Mission Planner, can I change the threshold?