Battey Usage Question

[caguy]

What is the best way to use a two battery system with a off-1-both-2 switch? I have two 110 amp deep cell batteries. I am never sure whether to use one then the other or both at the same time. I have an electric start OB so starting is not an issue. I have a stereo, VHS, GPSmap, led cabin and anchor lights and an autopilot.
I have a solar panel that charges both batteries with a dual controller.
I mostly day sail with occasional 4-5 day trips to Catalina.

Thanks in advance for your advice.

 

[dparilla]

There are tons of opinions as to what is best. If you do a quick forum search, or go to the musings with Maine Sail, there is currently a discussion on the various ways to use a two battery system.

 

[Stu Jackson]

Frank, it all depends on how it is wired. Does the AO go to the house bank or to the C post of the 1-2-B switch?

 

[caguy]

Frank, it all depends on how it is wired. Does the AO go to the house bank or to the C post of the 1-2-B switch?

There is no alternator. The solar panel runs to the controller and the controller goes to each of the batteries directly.

 

[Stu Jackson]

OK, Frank, then you most likely have the 1-2-B switch to do two things:

1. Select which of your two batteries or both are being used based on the switch position

2. the C post of the switch feeds the electric start and the electrical panel in your boat

So, your choices are simple: use one battery at a time, or use both. The advantages of using one at a time mean you always have a backup (assuming they both get adequately charged from your panel). Using both gives you a larger bank, but no backup.

Does that answer your question?

 

[Benny17441]

Everyone has their method which best may serve their particular needs. This is the way I use them. I only use one battery at a time while maintaining the second in reserve or as a backup. I only combine them on the eventuality that a boost is necessary to start the engine. This also protects against a bad battery damaging the other and against the eventuality of accidentally allowing both batteries to discharge. (All it takes is to forget to turn off the refrigerator overnight to wake up to dead batteries). I also alternate the use of the batteries with each outing to have the opportunity of exercising both and maintaining them in a similar condition as far as usage and remaining useful life. We carry a generator aboard which gives us the ability to recharge batteries practically at will so by design our battery bank does not need to be very large. As a matter of fact is similar to yours with two group 27 deep cycle batteries for a total of 210ah. The health of my batteries is measured by a results oriented method. All I need is for one battery to provide me power to run the refrigerator and instruments for 10 hours and still be able to crank the engine to be deemed to be healthy enough. When day sailing or coastal cruising I rarely exceed the 10 hour limit before anchoring and starting the generator or getting to a dock with shore power. For longer trips which might involve overnight passages we do make adjustments as running the refrigerator one hour on and one hour off and running the engine at intervals to motorsail and maintain speed while recharging. On occasions we may even carry a third battery and we always keep aboard a fully charged automotive battery pack. If we did not have the generator we would require a larger battery bank. To do a 4 to 5 day trip with just 220 Ah requires planning and a power budget.

 

[caguy]

Thanks all for you helpful suggestions. I will continue using them one at a time as suggested.