When using the moteino mega USB - is it OK to connect battery power (6V) to the vin and ground pins while connected to a computer via the usb jack at the same time ? I would only do this during testing/troubleshooting. The system needs to run on battery power when actually deployed.
Although I would still recommend taking it off if you are able, it is OK yes, there is a diode that blocks current going into the USB even if the battery voltage is higher.
A rule of thumb is to avoid powering something from 2 sources even if by theoretically by circumstance there should be no consequences.
Thanks, glad to hear a diode was included. However, I will avoid using two power sources whenever possible.