Two batteries with switch

[schmir]

I have 2 batteries on my boat with a switch with options of 1, 2 or both. Is there reason or preferred option I should be using. I used it on both last year. I took batteries out for the winter. I didn't write down where each one was hooked up. Will this make a difference when hooking back up in the spring? Thanks in advance for any help?

 

[JB]

Re: Two batteries with switch

Just be danged sure you hook positive to positive posts and negatives to negatives. If you use the "BOTH" position they are in parallel so it doesn't matter that they are in the same position.

 

[bruceb58]

Re: Two batteries with switch

Usually, the "both" position is used when one or the other batteries are discharged to the point where neither one can start your engine on its own. Putting them in the both position combines their remaining charge to get you started. You only want to keep them in the "both" position to allow them to then get charged at the same time.

You don't want to leave them in the "both" position when you are stopped. If you happen to leave something on, both batteries will get completely discharge leaving you no back up battery to get started again..

 

[schmir]

Re: Two batteries with switch

Does it make a difference which one I choose to use then? #1 or #2? Should I alternate which battery I put the switch on? Will I wear a battery out faster if I leave on #1 all the time?

 

[bruceb58]

Re: Two batteries with switch

Problem with leaving it on one battery all the time is the other one won't get charged. You can alternate...that would work.

On my boat I use a combiner. It is basically a relay that combines the two batteries when it senses that the alternator is putting out a hig enough charge voltage. Blue Seas makes one for less than $80.

http://www.bluesea.com/product.asp?Product_id=53476


The "old school" method is to use an isolator but you will never get your batteries fully charged because of the voltage drop.