Honestly, the same as if you run out of gas or diesel. With any boat, it’s a great idea to plan for these things with a tow membership if you are not watching your fuel/charge levels. If you burn out your entire charge on the high-voltage battery, as with a fossil-fuel boat, your 12v battery will still be fully charged, running your USB ports to charge your mobile, and running your VHF to support a distress signal or a radio call.