Without using a power module I want to confirm that is it OK to connect just a positive lead from one's LiPo pack to the signal pin of A1 as shown below to get voltage shown in the telemetry?
Note: I'm not using any type of power module, just a BEC for 5V power to APM 2.5 with JP1 connected.
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see http://web.archive.org/web/20130404091816/http://wiki.ardupilot-meg... for the pic.
You cannot exceed 5V on any of the Analog in pins. A voltage sensor is usually a voltage divider using two resistors. The APM PM does a divide by 10 on the full LiPo voltage. ie. 50V would generate the max 5V signal.
If you connected the cell closest to the GND wire from the LiPo you would not exceed this voltage. i.e.. it would be 4.2V max It would indicate the overall battery level, but if the cell is out of balance you could be thinking you had more energy left than you have or vice versa.
I still don't think it's a good idea, and using something like the ATTOPilot board is a better option https://www.sparkfun.com/products/9028