Newish sailor. ODay 28 with 2X 27M batteries. No solar.
Background: We are the habit of turning on engine, motoring for 10 minutes or so and then sailing with selector to #2 (drain is limited autopilot, VHF and Navigation). At the end of the day, we start engine from #2, dock, plug in and all is well. On a recent adventure, we anchored overnight, running lights and water pump sparingly (all on #2). Two false anchor alarms forced us to restart the engine at night. In the morning, battery #2 read 10 volts and could not start the engine. We were fine with #1.
Question #1: Does starting the engine consume a lot of energy? What is a rule of thumb time to keep engine one to '"top off" batteries? In other words, should the starter battery be left on alternator for more than 10 minutes? In other other words, did starting the engine twice without sufficient running time effectively drain the battery?
Question #2: How would one know when to replace a battery? Marine batteries can withstand deep discharges but how does one decide to replace? I am guessing it is a function of the stored energy but how to measure? I change a battery once but it was because it would not charge. I never attempted to measure the actual stored energy.
All help and comments appreciated.
Background: We are the habit of turning on engine, motoring for 10 minutes or so and then sailing with selector to #2 (drain is limited autopilot, VHF and Navigation). At the end of the day, we start engine from #2, dock, plug in and all is well. On a recent adventure, we anchored overnight, running lights and water pump sparingly (all on #2). Two false anchor alarms forced us to restart the engine at night. In the morning, battery #2 read 10 volts and could not start the engine. We were fine with #1.
Question #1: Does starting the engine consume a lot of energy? What is a rule of thumb time to keep engine one to '"top off" batteries? In other words, should the starter battery be left on alternator for more than 10 minutes? In other other words, did starting the engine twice without sufficient running time effectively drain the battery?
Question #2: How would one know when to replace a battery? Marine batteries can withstand deep discharges but how does one decide to replace? I am guessing it is a function of the stored energy but how to measure? I change a battery once but it was because it would not charge. I never attempted to measure the actual stored energy.
All help and comments appreciated.