Dual Battery Question

[5150abf]

Did I read somwhere that in a dual battery set up the batteries will only charge to the lesser batteries capacity?

I have 3 batteries on my boat, 1 starter and 2 mains, both large deep cycle, one is 3 years old and one is 3 days old and they are run is series so it is like one super huge battery.

Will they only charge to the older batteries capacity which is probably 70% now?

 

[bruceb58]

Re: Dual Battery Question

Hopefully your two batteries that you run in series are 6V batteries. Maybe you meant that they are in parallel if they are 12V.

If they are indeed run in parallel, that's not an ideal situation because it will only charge as high as the battery that has the lowest charge voltage. If you have one bad cell that is low by 0.5V it will severely limit the other battery charging. That is why both batteries have to be matched in size, age and in type.

 

[5150abf]

Re: Dual Battery Question

Yes they are parallel, I knew it was one or the other, I would notice pretty quick if I was running 24 volts.

And that is what I was looking for, I have a battery switch but haven't gotten to seperating the batteries, that is one of my winter projects.

This year I added a Motorguide 55lb wireless trolling motor and a Minn Kota deckhand so I added the extra battery to compensate and just threw it in line with the other battery.

Being November soon in Indiana I can't imagine it will be long till the boat is put away and I can get that fixxed.

 

[The Troll]

Re: Dual Battery Question

You need reserve cappacity for all trolling motor applications. To parallel 6 or 12 volt you do the same procedure. If you have a question on the condition of your batteries you can have them ( load tested ) at most any car or truck parts store. You could buy a hydrometer and test each cell but most times a load test will determine the condition of your battery. Since I do not know how you charge your batteries ( 1 single hand held, or an on-board charger) there is a hugh difference in the charging rates. Most newer on-board chargers have the cappacity to Smart Charge. They know what the battery needs, and maintains it at that level to charge correctly. All on-board chargers have internal grounds so you can run any 12 volt application from (1 ) of the batteries and not be concerned with to much voltage going to that application. Get your batteries checked, and if needed, replace the one that is weak.