Is the PX4 ready to use with current and voltage sensor?
E.g. the AttoPilot sensor or the 3DR power unit?
If yes - how to connect?
On the PX4 wishlist 
:
I2C able voltage and Hall-effect current sensor, with capacity of at least 6S and 100A.
By studying the board user manuals and schematics I have been able to find out the following:
Battery monitoring
Good and bad news:
Good: Battery voltage is per default measured on the battery Power input to the PX4 IO board, that two pole 7-18V Power in connector (see attached photo).
Perfect if your motor battery voltage does not exceed 18volt (~4S LiPo)!
Bad: The measuring only works if you power the PX4 assembly direct from your motor battery and the max input voltage is 18 volts. If you Power the PX4IO from a BEC you will just see the BEC voltage 
In my present project I use 6SLiPo to Power the motor - too high to connect directly to the PX4IO. Consequently I have to power the PX4 with a BEC.
Maybe there is a way to select an other ADC pin for voltage measurement by entering another value in the
MP parameter list for BATT_VOLT_PIN (default value 100 for PX4) ??
In order to use the PX4 FMU multi function connector pin 5 “Battery monitor” instead ??? :geek:
Current sensor
Good news: Connect it to the PX4IO “curr” solder pad, next to the Power in connector.
Excerpts from board schematics, indicating it might be possible to select an other voltage input for battery monitoring.
Useful if one for various reasons will not power the PX4 direct from the motor battery pack.
Just found official info about the analog pin assignment 