I was reading this question about an owner checking the alternator by disconnecting the battery, which is an easy way to validate on a gasoline engine. The single answer assumes that the OP is referring to a gasoline engine vehicle, but there is a diesel engine options for the vehicle.
It has been a while since I last played with any diesel engines, but they used to all have mechanically timed fuel injection, so once you get it running no electrical power is required to keep running.
Is this still the case? can you assume that all diesel engines don't require electricity to continue running, or do some now have electronically controlled fuel delivery that is dependent on an intact charging system?