Engine battery question.

Rapidroy5858

Member
Sep 23, 2018
82
LaPorte In.
Boat Info
1990 searay sundancer 270
Engines
Twin 4.3 mercruiser
I have to replace the sb battery in my sundancer 270da. When I purchased the boat it had 3 new deep cycle batteries 1 overcharged and fried. My question is do I need deep cycle batteries for the engines or will a good quality regular battery do the trick?
I know the deep cycle is best for the cabin and lighting.
Thanks for any advice!
 
For starting you are better off with a regular cranking battery. Deep cycles are only good for the house bank.
 
You will get multiple answers to your question.

Do you keep your boat wet slipped, on shore power with battery charger on..... or trailered?

Do you spend multiple days on the hook?

For me I like to have all my batteries the same so when the time came last year to buy new batteries I bought 3 deep cycle/starting AGM's to replace all of my flooded batteries.

Just to add.... you can get some really good AGM batteries for the price of a flooded battery. Check out Sams Club pricing.
 
I bet your last batteries were not deep cycle, they were likely dual purpose. If they had a value under cranking amps then they were dual purpose.

Look up the specs for your motor’s battery requirement and buy one that meets or exceeds it. Flooded cell will be fine, but the Sams agm are only $179 in a group 31.
 
I’ve hashed this out many times on this forum but there really is limited value in an AGM battery. Flooded lead acid will have more charging cycles but do require a higher level of maintaince. If you cannot maintain your batteries (location or otherwise) then AGM makes since. Otherwise your overall cost will be substantially lower per charge cycle with a flooded lead acid.

The next equation is brand... I’m not going to rehash it (search for my posts) but the short answer is buy a super premium brand if you want the overall lowest cost per cycle and the reliability. The premium brands ( mastervolt, rolls surrette, fullriver...etc) will have published depth of charge/# of charge cycles.

Don’t overlook your charger either. Make sure you have a smart charger.
 
I would personally replace all the batteries at the same time and check your charger. Dual purpose batteries would work good in your model boat.
 
I’ve hashed this out many times on this forum but there really is limited value in an AGM battery. Flooded lead acid will have more charging cycles but do require a higher level of maintaince. If you cannot maintain your batteries (location or otherwise) then AGM makes since. Otherwise your overall cost will be substantially lower per charge cycle with a flooded lead acid.

The next equation is brand... I’m not going to rehash it (search for my posts) but the short answer is buy a super premium brand if you want the overall lowest cost per cycle and the reliability. The premium brands ( mastervolt, rolls surrette, fullriver...etc) will have published depth of charge/# of charge cycles.

Don’t overlook your charger either. Make sure you have a smart charger.

You make many good points. However, for newer Merc engines with DTS and Axius, Merc requires AGM batteries. There are distinct advantages for power availability, depth of discharge, loss of charge during storage, and speed to accept a charge.
I also respectfully disagree that a wet cell can handle more cycles than an AGM. I believe it to be opposite and AGM can handle more.
But to the OPs post, a good quality dual purpose or cranking battery of sufficient capacity in MCA and RC is fine, flooded or AGM.
 
I would love to see some data to prove me wrong on the battery front. I am traveling tonight and tomorrow but happy to repost some manufacture’s data. Agm’s only real advantage is no maintance and some resistance to vibration because of the way the plates are packed. Take a rolls surrette wet cell deep cycle against any agm you find. Frankly, I would love to be proved wrong because I’ll buy that battery.

Now... to be technical there are better batteries. Lithium but that’s a whole different discussion.
 
Checked the battery that went bad it is a dual purpose, 1 year old had very little actual use as the boat sat till I purchased it in Sept. I suspect it was defective to a degree before it fried while plugged into the boat charger.
It's a brand I'm not familiar with, SBS is the manufacture, 1010 cca
 
So are you replacing the charger that fried the battery in the first place?
 
As far as replacing all batteries, as I stated they were all new last season so I'm thinking of replacing just the one that fried.
I will install new battery in spring plug in boat and check charging rate at all 3 batteries. I'm not clear on how the on board charging system works but im assuming it provides same amount of charge to all 3 batteries? I'm leaning towards installing a battery tender that will maintain all 3 at the same time. I have used them for years with great success and have read many negative posts about the original on board chargers that came with the boat.
I have the 2 remaining batteries on float chargers for the winter.
 
As far as engine starting batteries are concerned I personally believe that engine batteries should be stand alone and not on chargers. You engines alt charging system will keep them charged as required Good batteries will not go dead even after a month of non use.
The idea of having the batteries on constant charge is a flawed concept that can lead to that one last start when you leave the slip and dead batteries when you try to start the motor to return. This is because those with flooded cells did not do the required maintence on the batteries like checking fluid levels. Once the tops of the plates are exposed to air, there finished
 
As far as replacing all batteries, as I stated they were all new last season so I'm thinking of replacing just the one that fried.
I will install new battery in spring plug in boat and check charging rate at all 3 batteries. I'm not clear on how the on board charging system works but im assuming it provides same amount of charge to all 3 batteries? I'm leaning towards installing a battery tender that will maintain all 3 at the same time. I have used them for years with great success and have read many negative posts about the original on board chargers that came with the boat.
I have the 2 remaining batteries on float chargers for the winter.
What charger is on your boat? Newer Smart on board chargers are effectively trickle chargers once the battery reaches full charge. They also can send different voltage and current to individual channels based on battery state. If it cooked a battery, it is faulty. I have used on board chargers for 2 decades and never had one fry a battery. I get 6 years out of my batteries then change them for maintenance even though they still test ok.
As others mentioned. flooded cells need the water checked and filled or else...
 
tiara in the snow 01.JPG
What charger is on your boat? Newer Smart on board chargers are effectively trickle chargers once the battery reaches full charge. They also can send different voltage and current to individual channels based on battery state. If it cooked a battery, it is faulty. I have used on board chargers for 2 decades and never had one fry a battery. I get 6 years out of my batteries then change them for maintenance even though they still test ok.
As others mentioned. flooded cells need the water checked and filled or else...

I do the same. Thinking of doing batteries this year as they are 8 years old. A knowledgeable person I trust suggested not waiting too long as it is penny wise, pound foolish since the high output alternators on my Crusaders are expensive to replace. Better to do the batteries at 8 years than alternators due to overuse.
 
As far as engine starting batteries are concerned I personally believe that engine batteries should be stand alone and not on chargers. You engines alt charging system will keep them charged as required Good batteries will not go dead even after a month of non use.
The idea of having the batteries on constant charge is a flawed concept that can lead to that one last start when you leave the slip and dead batteries when you try to start the motor to return. This is because those with flooded cells did not do the required maintence on the batteries like checking fluid levels. Once the tops of the plates are exposed to air, there finished

I agree I'm on top of maintenance, checking battery water level and topping off with distilled water is critical.
The battery tender set up only charges as its required,that's why I like the idea of using one.
 
What charger is on your boat? Newer Smart on board chargers are effectively trickle chargers once the battery reaches full charge. They also can send different voltage and current to individual channels based on battery state. If it cooked a battery, it is faulty. I have used on board chargers for 2 decades and never had one fry a battery. I get 6 years out of my batteries then change them for maintenance even though they still test ok.
As others mentioned. flooded cells need the water checked and filled or else...
I believe it's the charger that came with the boat. I'm wondering if the battery was defective and was showing low voltage which in turn did not reduce voltage from charging system.
Again I will put new battery in , plug in the boat and read charge rate at all 3 batteries to see if they are all getting same voltage.
 

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