When the motor is running you should have the switch in the "both" position. Once you park and turn off the motor move the switch to one of the batteries to ensure that you have juice in one of them to start the motor to go home. It is suggested to not switch from one battery to the other while the motor is running.



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I am lazy and often forgetful. I have dual batteries and always have my switch on 1 or 2, never Both. I alternate this between 1 and 2 about once per month.

My theory: when in my slip, I am always charging both batteries via shore power. When running, I am only charging one battery and that battery will be used as house when anchored (no switching required). If there are any issues starting the boat, I can switch to the other battery which is charged from shore power (I typically only anchor one night, maybe two at the most). Up until this point, I've had no issues. To be honest, I don't want to forget about switching from Dual every time I cut the engine, I will be paranoid about running down both batteries.

Suggestions for the lazy and forgetful are most welcome!

 

Most of the newer battery switches have a make then break capability allowing you to switch from, let's say battery #1 to start, then to both to run and charge both. Whatever you do, check to make sure your model of switch is this type. It is never advisable to turn it off while running.

 

As others said, my switch, if turned from 1 to both to 2 or 2 to both to 1, will be "make then break" so the battery never drops. However, NEVER turn it through off with the engine on! It has potential to fry your alternator, and possibly other components if you have MPI.

 

Fishing boats and RVs are normaly equiped with an isolator that charges first the start battery then the trolling or dry camp battery. The trolling or dry camp can be completly discharged while starting remains fully charged. I am suprised to hear not all boats are so equiped. It's not a big job to retrofit if there is no reason not to.

 

I run on BOTH and when I get to where I am going I switch to 1 or 2 depending on the date. If it is an odd date then I use battery 1, even date I use battery 2. I feel that it evens out the batterys and you never have to remember what battery you used last.

 

You have asked some good questions but the last two can only be answered by you. "Or is one cranking battery and one deep charge for the cabin" you need to look at the batteries to determine what they are.
The first part of your question will depend on how your batteries are wired for use and charging. I leave my MBSS (master battery selector switch) on two. My "two" bank is 2 6v golf cart batteries, that interstate says I can start off of. My battery on #1 is a starting battery that is connected to my generator but is charged regardless of the position of the MBSS by my smart charger because I don't use the starting battery for anything but the generator or emergency starting so it is always charged.
I have a Link 1000 to monitor all my batteries and I get 118 amp hours of use from the house bank we get about 18 hours of draw while on the hook before we have to recharge but I do run a fridge, a 42LT freezer the necessary lights and have an electric head.

One battery should be a starting battery and one a deep cycle, the deep cycle used for playing the radio and lights. If you have a fridge I would not try and run it very long on one battery, it won't last. After a day on the water using the deep cycle for the radio and other electrical draws, turn them off switch the MBSS to the starting battery, start the boat and then switch the MBSS back to the deep cycle, this will cause the alternator to sense the needs of the battery that has been drawn down and replace the depleted amps faster.


Hope this helps you, I have spent as long as 7 weeks anchored out and you can't do that without good battery management.


Ken

 

This product for 120 bucks at Jim's will take care of all of the user interfacing with the battery switch. Turn the switch to on 1 and any time you start your engine the house battery gets charged there is no way for the starting battery if wired correctly to get drained.


http://www.boemarine.com/Blue_Sea_7650_Add_a_Battery-7650/