Can you run it off of the cranking battery? Yes. Everything in my boat electronically is run off of my cranking battery, 2 HDS's, head unit, amp and 4-8's, jack plate, power pole ect ect. However, I do have an over size cranking battery with excess CA and reserve capacity. I also replace and maintain this battery and TM batteries. I am able to watch the voltage level of the battery on my HDS as well as the Mercmonitor, which would both be good indicators of battery drain. If I got in a bind as a last resort, I could move over to a TM battery to get the motor started. I guess it really depends on your risk and tolerance level.