Battery Bank Setup

Tacoma290

Active Member
Oct 5, 2006
497
Tacoma, WA
Boat Info
340 Sundancer 2007
Engines
Twin 8.1 V-drives
Port/House Bank is two brand new Group 31 lead deep cycle batteries. Stbd/EIM Bank is two Group 27 lead dual purpose batteries installed in 2013. They are connected to an Intellipower PD2040 converter/charger.
I have been seeing volts only at 12.4 on the Stbd/EIM bank, while the other bank voltage is 12.6. So Stbd should likely be replaced as well. I know that the chemistry has to match across the banks, but does the Group number need to match for both banks? And does the type (starting vs deep vs dual) have to match for both banks?

I could not easily find how multiple bank chargers work. Is it one output to each bank? Or do the chargers use a different output for each bank?
 
Mostly just the type of battery since the charger can be set to different charging profiles like lead-acid, gel-cell, or AGM.

Are all the batteries in good condition? Not leaking? Water at the correct level? Do they pass a load test? I'd say if they are holding a charge above 12v you are still good to go and wait until they fail but that of course depends on your boating location and access to services if you are stranded.

I replaced all of mine at once. One failed a load test and the other was leaking and I had to use the emergency start button a few times so I replaced all 3 group 27 lead-acid with 3 AGM 31's Deep Cycle/Starting since they would fit.

Just be prepared for the weight. These suckers weight a bunch and to get the old ones out and the new ones in wiped me out while working laying on my stomach.
 

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Thanks for the reply, Ducky! Took the boat out this weekend, and the Starboard Group 27s would not hold a charge properly (12.2 volts after being on the charger and after a 30 minute cruise on plane).
So I replaced them with lead (so port and stbd remain both flooded lead chemistry) as soon as we got back. The Starboard batteries run the instruments and the Starboard motor, so I went with 2 Group 31 Fleet and Heavy Duty starting batteries. Duracell model SLI31PA from Batteries Plus ($124.99 each plus 10% off when ordered online). Have 950 CCA each.
 
So that means the current setup for my 340 is:
2 each Group 31 marine lead deep cycle batteries for Port / House loads, and
2 each Group 31 fleet lead starting batteries for Starboard / Electronics.
 
I was having similar issues in my 1997 330DA.

Port side originally had one blue top optima start and one blue top optima dual purpose. This was insufficient to run the house DC for very long.

I replaced with two new NorthStar Group 27s dual purpose on port/house bank.

previously I replaced the stbd dual purpose with a West Marine group 31 AGM. Gen Set uses a group 24 starting battery.
 
You shouldn't mix sizes within a bank. However, having 27s in one bank and 31s in another shouldn't pose any problems, as long as they use the same chemistry.
 
You shouldn't mix sizes within a bank. However, having 27s in one bank and 31s in another shouldn't pose any problems, as long as they use the same chemistry.


Sizes are the same in Port bank. Chemistry also the same on Port and Stbd. Gen Set has flooded battery instead of AGM, but has separate battery charger so it’s all good.
 
First Let's separate CCA/MCA from the conversation. These values have little to do with charging and only provide electrical current capability for starting.
Also note that AGM batteries are perfectly compatible with flooded lead acid charging profiles. The major difference is AGM will demand larger charge currents and consequently provide the benefit of shorter charge cycles provided the charger or alternator can support the electrical current demands. It is because of the rate of charge and float voltages that AGM batteries should not be mixed with flooded batteries while using a typical charger set for flooded battery charging. The same holds true in mixing different sizes of a technology such as connecting a 240AH Group 8D and 90AH Group 27; the charger will never be able to fully charge one of the batteries consequently, you would rely on the batteries themselves to self-balance to a charge level somewhat below full charge; this no doubt will sacrifice the life capability of a battery. Additionally, one would never know the depth of discharge (DOD) of any single battery which is the primary determinator of the life of a battery. Then to a multiple bank setup where one bank is say two Group 27's and the other bank is an 8D. It then becomes the responsibility of the multi-bank charger/converter's capability to independently monitor the state of charge and establish the appropriate charge profile for for the battery banks independently which most modern multi-bank chargers can do; however, the temperature monitor must be installed on the smaller of the two banks. Where it becomes problematic is in the cases where a single bank charger is utilized through an isolator to charge multiple banks. The SR 550DB is such a configuration. So unless a graduate in 400 level of battery school it's best to maintain the same battery technology, size, and age in a bank. And, to know the capability of the charging system if differing batteries are in a multi-bank configuration.
Tom
 

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