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Author Topic:   12V versus 24V Battery
La Samba posted 03-28-2009 01:14 PM ET (US)   Profile for La Samba   Send Email to La Samba  

This is my first post as a happy new owner of a '92 Montauk 170. I am new to boating and having purchased this boat last fall,this will be my first full season of use. I have a question regarding marine batteries that I could use help with. As I was starting to go through my equipment getting ready for spring boat projects I thought I should get my battery out of storage and check its charge. I noticed for the first time that it is a 24V deep cycle marine battery and my motor is a 90HP Johnson with oil injection that is listed in the owners manual as a 12V motor.

When I checked, the charge on my 24v it was at 12.25V. Is this improper to be using a 24v battery with what seems to me to be a 12v system? I have a GPS and marine radio and plan to add a small amp and speakers for an Ipod hookup. Now I'm not sure what I'm dealing with.

Any insight or further explanation of battery function and 12V vs. 24V would be greatly appreciated.


Chuck Tribolet posted 03-28-2009 02:45 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
That's the battery that came out of the boat in the fall, right?

Are you sure it's a 24V battery? How many battery caps does
it have? 12V will have six, 24V will have 12.

There's a battery SIZE (dimensions) called "Group 24" that
is the most common size to use in that vintage and size
of boat. It's a 12V battery. I'm guessing you read
"Group 24" as "24V".


jimh posted 03-28-2009 02:48 PM ET (US)     Profile for jimh  Send Email to jimh     
You may be confusing the battery voltage with the battery group size. It is very common that 12-volt batteries are made in a Group-24 size case.

In the odd event that you really have a 24-volt battery, if its terminal voltage is only reading 12.25-volts the battery has been ruined. However, I doubt that this is the case. It is much more likely you have a 12-volt battery.

Check the labeling on the battery carefully to determine if it is really a 24-volt battery. If it is truly a 24-volt battery, you should not try to use it with your boat. The Johnson outboard motor and all electronic accessories you would like to power require 12-volts, not 24-volts. The only time 24-volts is commonly used is with electrical motors in auxiliary trolling motors.

The Boston Whaler 170 MONTAUK was not made until 2002, so it is unlikely you have a 1992 model. You probably have a 1992 MONTAUK 17, a classic and fine boat.

La Samba posted 03-28-2009 03:23 PM ET (US)     Profile for La Samba  Send Email to La Samba     
Chuck and Jim H - Thanks for your quick reply. Yes, the battery in question came with the boat when I bought it from a private seller. I re-checked the battery label and here is the info:

Battery is an "EverStart RV Marine" deep cycle by Walmart. It is labeled 24DC-6 Trolling Deep Cycle. Amp Hrs: 75 , Crank Amps 525, Cold Crank 405 amps.

As for number of battery caps, it has two rectangular caps that are removable - each accesses three cells.

To me, the labeling still implies 24V but perhaps the 6 cells confirms it as 12V?

I'm going to go to the Walmart website now to see if I can look up the specific model and confirm.

Last fall, all equipment - GPS, marine radio, lights, bilge pump were in perfect working order. I guess this is further evidence that the battery is 12V.

Thanks again for your response. I have a long list of projects and expect to be using this forum for good information to hopefully keep me out of trouble!

La Samba

dbrown posted 03-28-2009 05:01 PM ET (US)     Profile for dbrown    
It is a 12 volt deep cycle battery. "24" is the group number. Walmart does not make a 24 volt battery to my knowledge. You would be better off getting a cranking battery for starting your engine and leave the Deep Cycle battery for trolling motor duty.
swist posted 03-29-2009 06:08 AM ET (US)     Profile for swist  Send Email to swist     
I disagree. Any deep-cycle battery can start an outboard easily. And the deep-cycle battery is advantageous from all other aspects - particularly if you need power while the engine is not running. Electronics, stereos, lights, trolling motors, etc are all things you might want to run on a boat with engine off. You run a starting battery down just a few times and it's gone.
La Samba posted 03-29-2009 07:28 AM ET (US)     Profile for La Samba  Send Email to La Samba     
I must say that I am very safety conscious as mine is a family boat with three kids and I'm boating on the coast of Maine. One of my biggest concerns is motor failure or running down the battery while trying to solve a problem while out on the water. I have oars and a mount for a kicker motor which is on the wish list but making sure I have an optimal battery setup seems like a critical part of avoiding a potentially bad situation. I carry a portable 12V power source that I keep fully charged and is probably good for a limited amount of starting attempts in an emergency but I am interested in having a second battery on board.

I am set up with a battery switch that has "battery 1", "battery 2", and "both battery" positions. I would like to put a second battery on line and set it up and use it in a way that keeps both batteries optimally charged. I need to explore the small boat electrical forum to look for further info on this. However, any advice on this would be a big help.

La Samba

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