Sending battery status to Pixhawk

We use systems on our vehicles that are much higher voltage compared to the usual 0-100V systems. And so we want to find a way to send our battery information back to the board using a method other than the ADC. I tried to use the mavros topic with /mavros/battery but it has no subscribers and so my publishing script did not achieve anything at all.

Is there an interface on the hardware other than the ADC to achieve this functionality?