I've read the instructions and searched this forum, but have been unsuccessful in finding an answer to my problem.

I'm running a 4 cell 5000 maH battery that measures 16.8 Volts when fully charged and plugged in to my 3DR Hexacopter equipped with an APM 2.5 controller.

I've measured the BEC voltage from the ESCs going to the APM input at 4.92 volts.

Now my problem:

In the Calibration box, there's a place to enter the APM input voltage.  I set that to 4.92 Volts.  There is another place to enter the measured battery voltage.  I entered 16.8 Volts.

When I click to another function in MP and then return to the battery monitor setup, the 'Measured battery voltage' is never saved.  Each time I do this, my original setting of 16.8V is gone there is some random voltage in its place.  Plus the box is greyed out so nothing can be entered.   The APM input voltage stays at what it's supposed to be.

Below is what I see after I've entered all the settings, gone to another routine in MP and then returned to the battery monitor setup... In this case it says 20.308V but it is different each time I look at the battery monitor page.   

Any ideas of how I can get the Measured battery voltage setting that I enter to stay ??

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Are you measuring this 4.92 on the APM board?

Was THIS the section you followed in the Wiki?


Yes..  I used those instructions.  But I cheated and measured the Vcc line on the Outputs.  (My board came in the plastic case and at the time I was too lazy to pull the case apart :) )   I did the test on the diode and have 5.01 volts.

I entered the new input voltage and somehow (magically) the routine is remembering the battery voltage.

I'm not quite sure what happened when I first tried this..   Thanks a lot for your help!


One thing I have to remind myself is that what I see on the MP screen has to be sent to the APM, APM accepts and stores it, and then it is confirmed back in MP.

You were fine checking it on the Output rail IF JP1 is installed.

For more information you can take a look at the Simplified 5V/Vcc schematic HERE.


Hi, I am having exactly the same issue. No matter what I do, I cannot get it to save the calibrated voltage. Do you have any idea what you did to fix it please?

The wizards in MP just change a bunch of parameters in a reasonable way (so that, ideally, you don't end up with absurd or inconsistent param values). However, you can just simply go and change the params directly (Config / Tuning Tab and then Full param list or Tree, personally, I like Tree as it chunks the params into easy to understand sections). The param list is here and the one you are after is I believe BATT_VOLT_MULT under BATT_parameters. Remember that, unlike the wizards, these changes need saving into the vehicle so write parameters (button on the right) and then Refresh to verify if the change has gone through. Another wise thing to do is to save your existing params into a file before you edit them (again, buttons on the right).

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