I'm new to electronics and here's a circuit I've put together for powering a pi / arduino and related gear.
9.6v battery pack 1 -> 5v BEC -> USB port -> Raspberry pi (via mini-usb) -> Arduino Mega (via usb)
On the arduino mega I have 2 signal pins, 8 and 9, going to two continuous rotation servos. The ground for one of these servos goes to the arduino ground. I then connected the arduino ground via another pin to my breadboard and the second servo is grounded here.
On the breadboard I have a second 9.6v battery pack which is going to the breadboard's power terminal and sharing ground with the arduino. Both servos are powered from this board (the +5v from the second battery pack)
This works and the BEC's are protected against reverse voltage, however when I just connect the battery pack for the pi/arduino I see a light come on on my BEC regulating the servo +5v. The servos will not run until I connect my second battery pack, however I still feel that this is less than ideal and I might do damage to some components long-term.
Is there a safer way to do this circuit? Apologies for not having a diagram but I sort of threw this together as I went and I did try to draw a diagram but I got quite confused with how to draw the grounds