Let’s talk batteries.

lrdchaos

Petty Officer 1st Class
Joined
Feb 11, 2008
Messages
265
Recently picked up a 2015 Monterey 238ss with a 350mag that has a dual battery setup. It’s the manual switch that I can manually sellect 1 or 2 or both. The boat currently has two deep cycle batteries with 875cca, which should be sufficient since the 350 only required 550cca I believe.

Ive never had a boat with a dual battery setup. Is there an issue with starting the boat at the first of the day and running with the switch on both? The. When we get to where we are going switch it to battery 1 or 2? I understand that I will have to switch off both so I don’t drain both batteries down throughout the day? Once we are through and headed home start the boat with the battery that’s been running the radio and let it charge back to the ramp? My goal would be to use battery 1 on odd days and battery 2 on even days to cycle each battery.


I understand there is an automatic system that does battery switch and charging, but after buying and tagging the boat I would like to use it before I spend more money on it.
Thanks
 

paulswagelock

Petty Officer 2nd Class
Joined
Jan 10, 2018
Messages
100
Your plan is fine and would work. I am not a fan or running on both only because a catastrophic failure of a battery could kill both as you run across the water and you would be stranded. Small chance but still a risk. Could consider just running one and switching each time you use the boat. Look into a Yandina 100 combiner - low cost and solves your problem.
 

alldodge

Moderator
Staff member
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Mar 8, 2009
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42,346
What you want to do is fine. Being a 2015 it should have a make-before-break switch. Which means as the switch goes from one bank to another or both, the connection is made before it breaks with the other. This is done to protect the alternator.

To verify look up your switch model to see if this happens. If it does then after the motor is started you can switch to the other bank or both.

The Yandina is a automatic charge relay (ACR) like the Blue sea model
 
Joined
Mar 1, 2005
Messages
956
Maybe I'm old, but what is the merit of the boat using deep cycle batteries for starting the boat? I would think that one battery would be a normal "starter" battery for cranking the motor and running various things such as radio, running lights, and graph/sonar/gps. Your other battery(s) would be deep cycle for running trolling motor, beer fridge, etc.
 
Joined
Mar 1, 2005
Messages
956
What about the voltage issues that can pop up? I guess that I would double-check what the manual for the engine says because it's not just as easy as more capacity/life. Deep cycles have a tendency to have bigger voltage drops during motor cranking that can affect the fancy modules (such as ECM) in newer motors.

It will all probably fine here but it's worth noting. A deep cycle will be okay on 75% of boats/motors but can cause problems with others.
 

JimS123

Fleet Admiral
Joined
Jul 27, 2007
Messages
8,187
Maybe I'm old, but what is the merit of the boat using deep cycle batteries for starting the boat? I would think that one battery would be a normal "starter" battery for cranking the motor and running various things such as radio, running lights, and graph/sonar/gps. Your other battery(s) would be deep cycle for running trolling motor, beer fridge, etc.
You start your car multiple times each day, so a cheepie wally battery is OK. But your boat has limited use, thus it needs to be a good one because its not charged up regularly. Even a deep cycle battery will lose its life if discharged many times below 50%.

The optimum starter battery on a boat is a dual purpose. Cranking power, PLUS deep cycle. If you have a second battery dedicated to "stuff", a deep cycle is preferred.
 

dingbat

Supreme Mariner
Joined
Nov 20, 2001
Messages
16,158
Deep cycles have a tendency to have bigger voltage drops during motor cranking that can affect the fancy modules (such as ECM) in newer motors.
Cold cranking amps (CCA) is the number of amps a 12-volt battery can deliver at 0°F for 30 seconds while maintaining a voltage of at least 7.2

"Deep cycles" tend to have a lower CCA for a given (battery) case size, but there is no difference in output between a 675 CCA rated deep cycle and 675 CCA rated starting battery.
 
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