How to choose the size of a Marine Battery ?

[Got a Boat]

I have to get a new battery, Can you just grab one of the bigger batterys when you also wannt to run an electric motor with it ? can the battery be too big.<br />Is there a way to figure out if you know the motor is charging 18amp. So then you could charge in 3hour running motor a 54amp/h flat battery ? is this right ?<br />Would it make sense to have two batterys on the boat ? one smal one wich is there for the Starter motor only and have a bigger one for all other electric equipment e.g. lights, sounder and electric motor. A automatic switch or relay disconects the larger battery whewn the motor is not running/charging.<br />Wer do i get such a relay for our boat ? or does it get too expensiv having a dual battery ?<br />Thank you for any tips

 

[roscoe]

Re: How to choose the size of a Marine Battery ?

I would go with two batteries, keeping one for starting the main engine and the bilge pump.<br /><br />You can use one of these: click. <br /><br />You are going to have to run at WOT for a long time to charge a low deepcycle battery.

 

[OBJ]

Re: How to choose the size of a Marine Battery ?

Yep...what roscoe said. And be sure to get Marine Batteries. There are differences between car batteries and marine batteries. And don't skimp on cranking power.

 

[18rabbit]

Re: How to choose the size of a Marine Battery ?

I agree with what was already stated, split the battery applications. If you don’t, definitely get a large, dual purpose, AGM battery. Look for the brand name Concorde as a first choice and Deka (East Penn Manf) as a good second choice. Size? Depends on the condition of your back…get the biggest one you (and a friend?) can handle. If splitting the batteries, Concorde is still an excellent choice for a starting battery but Surrette (Canada)/Rolls (America) is my first choice for deep cycle and Concorde is a good second choice in this application.<br /><br />BTW, your alternator is not going to completely charge your battery(s) no matter how long it runs. You are going to want to use a multiple-stage charger when you get back to the barn. If you do not use one of these, don’t waste you $$$ on the quality batteries I mentioned above. Instead, get the cheapest battery you can and think of it as a consumable, throwaway item. (Also, about your math…not all the energy goes back into the battery. Knock off about 20% for inefficiency.)<br /><br />Quality batteries cost more initially but actually save you $$$ in the long run. The Surrette/Rolls has a 10-year warranty. They have been in use for 12+ years. Pay twice as much but your battery will last 3 or 4-times as long. Problem is not just $$$, the bigger problem is when the cheaper batteries crap out on you. It won’t die until you are really, really need it…says Murphy. <br /><br />OBJ is right on about the suggestion of a marine grade battery. Unfortunately, the batteries you get at places like Walmart are not really ‘marine’ grade.

 

[OBJ]

Re: How to choose the size of a Marine Battery ?

Hey rabbit....ain't never heard of a Concorde or Deka battery. HMMMMM....maybe I oughta' get out more often.

 

[18rabbit]

Re: How to choose the size of a Marine Battery ?

Concorde:<br /> http://www.lifelinebatteries.com/marinebattery.asp <br /><br />Surrette/Rolls:<br /> http://www.rollsbattery.com/ <br /><br />Deka:<br /> http://www.dekabatteries.com/products/marine.html <br /><br />EDIT: Anyone that is serious about deep cycle battery applications on their boat should be running a series of 6v batteries. They are manufactured with thicker lead plates, cycle deeper with less damage, and designed to take max punishment. See the battery box for a pair of 6v batteries (golf cart):<br /><br /> http://www.bluesea.com/Products/BB/BB.htm

 

[ThomWV]

Re: How to choose the size of a Marine Battery ?

This is really absurd. Absolutly no one alive can tell you what kind of battery you need with the information given. First off to be able to suggest a battery type or size its essential to know what kind of boat its going in, what sort of power the boat has, and most important, how the boat is used.<br /><br />Next thing. You never have to run an engine at WOT for the alternator to put out its maximum power. Almost all of them will be putting out their maximum electrical power by the time the engine reaches 2,000 RPM.<br /><br />Next thing, for the vast majority of small boats one of the most foolish ways you can wire up the batterys is to have a separate "Starting" battery and then some sort of "house" battery. <br /><br />Next thing. Yes, two batterys on a boat, any boat, is a lot more than twice as good as one battery. If you don't believe that try starting your engine by pulling a rope sometime, particularly if it happens to be a big V-6 outboard.<br /><br />Next thing. Most batterys do not die becuase their useful life, in terms of charg and discharge cycles, has been reached. Most batterys die from lack of maintainence or simple abuse. That being the case it makes almost no sense at all to buy one of the super expensive batterys, because you can kill one of them prematurly just as easily as whatever Wal Mart has on the shelf.<br /><br />So tell us, what you got and how do you use it?<br /><br />Thom

 

[OBJ]

Re: How to choose the size of a Marine Battery ?

Well, Thom, on behalf of 18rabbit, roscoe and myself, let me offer a cincere apology for being "absurd". <br /><br />To suggest that you get as good a battery as possible for your boat, IMHO, is not absurd. You may not need as many CCA to crank a smaller engine as you do a larger engine, but the extra helps. Carry a spare? Why not? I use a 850 Trojan cranker for my 90hp and two Trojans Deep Cyles for my trolling motor..it's a 24V. I also have a battery switch connected to on of the deep cycles "just in case" the cranker goes south.<br /><br />Gotta disagree with ya' on the charging at at 2000rpm. It all has to do with the magnets spinning around the coils setting up flux fields and all that electrical stuff. The more the magnet pass's a coil, the more flux is set up...hence more output.<br /><br />I will agree though that most folks don't know how to treat a battery to get the most for their buck. They usually blame it on the battery when a little trickle charger could have saved them a new battery.<br /><br />But again...if our suggestions seem absurd...well...just consider the sources and pop another top.

 

[18rabbit]

Re: How to choose the size of a Marine Battery ?

Thom – give serious consideration to moving your pompus @$$ to another forum.

 

[sloopy]

Re: How to choose the size of a Marine Battery ?

Well how DO you choose a battery?

 

[OBJ]

Re: How to choose the size of a Marine Battery ?

Sloopy you sonavagun, how are ya'? Things gettin' good up on Cheat?<br /><br />All motors have a recommended CCA. My 90hp is recommended to have at least a 650CCA battery for starting. I usually go 200CCA higher if possible. The smaller engines won't need as much. But sure is nice to have the extra there.<br /><br />Don't be to hard on Thom, rabbit....maybe he's just having a bad day. We all do on occasion.

 

[sloopy]

Re: How to choose the size of a Marine Battery ?

Your outboard needs 650 cold cranking amps and you get a 200 cold cranking amp battery? Thats a lot of amps for that little starter motor to pull and for that battery to supply :-D

 

[sloopy]

Re: How to choose the size of a Marine Battery ?

And I am doing fine, what about you?

 

[Drowned Rat]

Re: How to choose the size of a Marine Battery ?

He goes 200 Higher or 850A.

 

[sloopy]

Re: How to choose the size of a Marine Battery ?

Woops I miss read it. Rat do you just hang around jey waiting to jump on post? :-D

 

[ThomWV]

Re: How to choose the size of a Marine Battery ?

18 Rabbit,<br /><br />As long as there is as much misinformation floating around as I have seen lately I think I'll just stick my pompos *** right here and try and clear a bit of it up.<br /><br />The point I'm trying to make for the guy is that you should be buying a battery based on the situation it will be used in. In this case Got A Boat hasn't told us anything about what he is going to use the battery for. Its a lot different picking a battery for a 50 horse power Mercury on the back of a john boat than it is picking a battery for a guy who gigs flounder with lights at night or a guy who runs a ski boat with no electronics at all and never sees the dark of night with it. To tell the guy in the latter boat that he is best served with a brace of golf cart batterys is plain stupid, to tell him that an Absorbed Glass Matt battery is the best thing since canned beer is equally absurd. At the same time telling a guy with twin diesels in his cruiser that a pair of lead acid Group 24's is the ticket would be a hugh mistake as well. There no One-size-fits-all in batterys for boats or for anything else. So until Got A Boat gives a bit of information about his use - like what engine he has, what boat its bolted onto, how he uses the boat, and what sort of electrical demands he puts on the battery - there is just no way on earth that anyone can give him any meaningful advice at all. If he's got a 12' john boat with an electric start 25 hp outboard there isn't much likelyhood that he needs an AGM battery or a brace of golf cart batterys wired together either. <br /><br />Thom

 

[Drowned Rat]

Re: How to choose the size of a Marine Battery ?

Rat do you just hang around jey waiting to jump on post?

What?

 

[sloopy]

Re: How to choose the size of a Marine Battery ?

There was one minute between the time I posted and the time you posted.

 

[Drowned Rat]

Re: How to choose the size of a Marine Battery ?

Sloopy. Did you ever get your briggs and stratton running again? Last I heard you had a problem with the leg or something? Have you had it in the water this season yet? I really like mine so far, no problems. It scoots my canoe along pretty good.