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Author Topic:   Dual Batteries for Montauk 170
gorji posted 08-07-2006 10:31 PM ET (US)   Profile for gorji   Send Email to gorji  

I've installed a 1,2,All,OFF swtich along with a second redundant battery for my Montauk 170. I have read the tutorial by JMH @

I would like to know if:

1. I want to have a starting battery in Bank 1 and a deep cycle battery in Bank 2. My understanding from the article is that the batteries need to be similar. At first I thought of putting a "hybrid" battery in bank 2 but I really want a deep cycle battery for bank 2. Bank 2 will be used for consuming current while not underway.

2. Do the batteries in both bank need to have similar cranking amps? I understand that they need to be similar (NO AGM on one bank and wet battery on other).

Thank you

Bulldog posted 08-09-2006 04:25 PM ET (US)     Profile for Bulldog  Send Email to Bulldog     
The batteries do not have to be the same amp rating. The batteries should be the same type as I've read that several places, also chargers usually state something along that line also.Why not go with the dual-purpose batteries and get the 1000 amp size, which can still be the small case size. You might need that second battery to start the engine.....Jack
gorji posted 08-10-2006 08:19 AM ET (US)     Profile for gorji  Send Email to gorji     
Thank you.
Uhhhhh. I just purchased a Sears Die Hard Deep Cycle for bank 2.

I will further investigate this issue. Maybe I'll return it. What do the big cruisers do? Don't they have banks of deep cycles and 1 or 2 starting batteries? They all have to be the same?

jimh posted 08-10-2006 09:00 AM ET (US)     Profile for jimh  Send Email to jimh     
The electrical installations on large vessels with inboard engines and much greater electrical loads in their house circuits are more complex than those found on small recreational vessels. Also, such installations are beyond the scope of the discussion here, which, as you recall, is SMALL BOAT ELECTRICAL.

I suggest you re-read my article. You seemed to have drawn some conclusions from it which are not intended. The advice in the article regarding the problems encountered in using batteries of different type and age is all in reference to what may happen when the batteries are operated in parallel. The article specifically cautions against extended operation with the batteries connected in parallel. The article on wiring of dual battery switches is intended to show a few possible configurations. There are many more configurations which can be used. The ones shown are simple, straightforward circuits which can be easily understood. In general, I find that there is little value in having a complex and sophisticated battery primary distribution wiring system if the operator of the vessel is not able to understand and operate the system. On a small boat there generally is not a need to install complex systems of multiple batteries.

It is not necessary that all batteries in an electrical system be of the same type and age, nor is such a recommendation given in my article. The specific focus of my article is to highlight some problems which can occur with twin engine installations.

The primary purpose of the battery on a small boat is to provide starting current to start the outboard motor. If you have an outboard motor which can be started by hand or pull-starting, you may not require a duplicate or redundant starting battery.

I recommend you install the primary battery distribution wiring in your small boat as you see fit, but be sure that you thoroughly understand how the system is configured and how to operate it.

gorji posted 08-10-2006 08:27 PM ET (US)     Profile for gorji  Send Email to gorji     
Thank you for your article, this wonderful website, and your clarifications.
jimh posted 08-10-2006 11:49 PM ET (US)     Profile for jimh  Send Email to jimh     
Gorji--Thank you for the kind words about the website.

Check with your engine manufacturer to see if they have an secondary charging kit which can be added. Many outboards can charge two batteries at once. If you can add that facility to your installation you will be sure to keep both batteries at a high state of charge.

gorji posted 08-10-2006 11:54 PM ET (US)     Profile for gorji  Send Email to gorji     
I had the dealer put 2 batteries in along with a 1,2, ALL, off switch. I asked if the 90 HP motor can charge both and was told yes, no problem.

Now only if I could understand the wiring for the switch. There is always something!!

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