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Author Topic:   Dual Batteries in a Montauk
eportfolio posted 08-13-2007 09:10 AM ET (US)   Profile for eportfolio   Send Email to eportfolio  
I only have one battery on my Montauk, but am interested in having 2. What is the configuration for having 2 batteries and how are they used? Is one dedicated to starting and the other to electronics? Are they both connected to the engine so they both take advantage of the alternator recharging?

Sorry for the naive question...still learning.

jimh posted 08-13-2007 02:09 PM ET (US)     Profile for jimh  Send Email to jimh     
A typical wiring arrangement for a single engine boat with dual batteries is shown in

but there are many variations possible to permit more sophisticated isolation of electronic loads from the starting battery and more automatic charging of both batteries. To describe those arrangements is beyond the scope of this reply and will require a lengthy illustrated reference article.

eportfolio posted 08-13-2007 02:48 PM ET (US)     Profile for eportfolio  Send Email to eportfolio     
Excellent! Thanks Jim.
sternorama posted 08-16-2007 12:46 AM ET (US)     Profile for sternorama  Send Email to sternorama     
I have two batteries on my Nauset. They are connected to a switch so that you can pick which one (or both) is getting and or giving the juice. I have my VHF radio attached to the second battery directly so that it is always powered.

There is another device that you might be interested in that is a two battery maintainer thinky... both batteries connect to it. It manages the recharging current such that first the starting battery is topped off, then once it reaches the acceptable voltage the second battery is automatically charged. No manual switch is needed.

I have a new one still in the package, If you are interested I'll sell it for a good deal. West Marine sells (or at lleast used to) sell them.

Henry posted 08-16-2007 01:38 AM ET (US)     Profile for Henry  Send Email to Henry     
The real problem is where to locate the second battery.
dburton posted 08-16-2007 04:55 PM ET (US)     Profile for dburton  Send Email to dburton     

Jimh wrote a good thread on ACR’s. Here it is:

Boating Magazine (June 2007) had a two page article on adding a second battery. It is based on using Blue Sea’s “add a battery system” that uses an automatic charging relay (ACR). I scanned the article and would be happy to email it to anyone.

dburton posted 08-16-2007 09:31 PM ET (US)     Profile for dburton  Send Email to dburton     

Here is a link to the blue sea product info on the "add a battery system". I plan on adding this or something similar to my Dauntless 160 this winter.


Casco Bay Outrage posted 08-17-2007 05:34 PM ET (US)     Profile for Casco Bay Outrage  Send Email to Casco Bay Outrage     

Consider that a second battery is warranted when you have a lot of electronics and want to spread the load. Having just a VHF, GPS, Fish finder is not, in my opinion, cause for a second battery.

If you want the added redundency for starting, a second battery is an option.

Let's not forget that most 90 hp engines can be rope started. I rope started my 1987 Yamaha 90 several times when I left things on by accident while at a mooring. My 2003 Yamaha 115 4-stroke has a starting rope. I have not actually used it.


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