Garmin Livescope will draw as much as 8 amps per hour.  It requires a 12V, 46 Ah battery, which should provide around 8 hours of run time.  A smaller  23 Ah battery will deliver around 4 hours of run time. Boat owners have a variety of battery set-ups on board, and can often have many items drawing power. Weather will also play a role in battery efficiency. The abovementioned run times are indicative under normal circumstances but will vary based on your specific circumstances.