Can I use a car battery for my mercruiser?

mjgates

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May 5, 2010
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I have a 5.0 I/O mercruiser. Can I use a car battery, or is there a benefit to using a marine battery?

Thank
 

Navigator_Victory

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Apr 3, 2011
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Re: Can I use a car battery for my mercruiser?

Car battery is not designed for deep discharges and or frequent discharges so the life of the battery will be very short.....it should start the engine and work just like any battery but, the life will be very short.

More importantly why not use a marine battery on your car.....
 

Faztbullet

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Re: Can I use a car battery for my mercruiser?

A automotive battery usually does not have the reserve hours or MCA amps as posted earlier. It also does not have the internal supports for the lead plates to pervent damage from sudden impact do to rough water.
 

Lodgepole

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Re: Can I use a car battery for my mercruiser?

I take the other side. Automotive batteries have more cold cranking amps than marine. Longer and better warrenties. Many have 3 year free replacement. Most boats have the battery in the stern and therefore doesent get jarred any worse than does a battery in a car on many of the roads we drive on. I might consider a deep cycle marine battery for running a trolling motor. But for just engine starting, my money is on an automotive battery. You start a car every time you turn arround and the battery holds up. Your boat has an alternator just like a car and will keep your battery up. Automotive battery has worked for me for 58 years without a single failure.
 

paultjohnson

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Re: Can I use a car battery for my mercruiser?

I vote for using a Marine Starting Batt, not a deep cycle, thats if you are just concerned about starting and are not going to be sitting for hrs with the engine off and a stern light and assorted other electronics on. A marine batt should be built to withstand the jarring better, to keep the lead plates in place, as previously stated, weather its a starting or deep cycle. My 86 4.3 does seem to turn over better with a starting batt as opposed to a deep cycle. For whatever reason. If i had a car batt lying around, I would use it, if I was buying new, it would be marine rated...
 

Brewman61

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Re: Can I use a car battery for my mercruiser?

Let's get our terminology straight. A marine battery is simply a battery specifically made for marine use. One type of marine battery is a marine cranking battery, similar to a car battery. This type of battery is not made to be repeadedly discharged and recharged. It's intended use is to provide a short burst of high current for cranking over engines.
They are made to be kept charged. Repeated discharge/recharge will shorten their life a lot. That is one type of marine battery.
A deep cycle battery, which is also a marine battery, is made to provide a relatively long steady source of power, and can be repeatedly charged and discharged without damage. Like the constand demand of an electric trolling motor.
So it depends on what you want to do with your battery. Crank the engine? Use a cranking battery. Wana drain and recharge? Go deep cycle.
Deep cycle batteries don't provide quite the high current burst that cranking batteries do, thought in many cases they can start an engine. The term "marine" can be applied to both types.
 
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rickryder

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Re: Can I use a car battery for my mercruiser?

Can't argue with that^^^^^
 

JaseBosto

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Re: Can I use a car battery for my mercruiser?

I went marine DEEP CYCLE only because when I go out on the lake on a nice summer day I like to leave the radio on, and it stays on for hours sometimes...then theres the nights when I leave the radio on and lights too. If I threw anything but a deep cycle in I would have to do that less.
 

mjgates

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Re: Can I use a car battery for my mercruiser?

Thank for the replies. I think I will go with a deep cycle marine battery since I power an audio system with amp, sub, and tower speakers, and often keep it on for sustained periods while we are swimming.
 

ejnichol

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Re: Can I use a car battery for my mercruiser?

Brewman has it correct.

Only thing I'd add thats a major difference is marine starting has additional threaded post for accesories and automotive starting just has standard large round terminals for cable ends but no provision for adding extra wires.

If you want maximum cranking power get the marine starting or automotive in correct case size to fit your tray.

Remember to periodically charge your battery in off season.
 

stonyloam

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Re: Can I use a car battery for my mercruiser?

Thank for the replies. I think I will go with a deep cycle marine battery since I power an audio system with amp, sub, and tower speakers, and often keep it on for sustained periods while we are swimming.

With all of that stuff you might be better off adding a second battery for your accessories. The deep cycle battery is not designed to deliver high cranking amps for starting, and after a few hours of running accessories might not be able to deliver what you need to start. A reasonable solution is to have a good high cranking amp starting battery wired to the starter (auto should be OK) and a second deep cycle battery to run the accessories, along with a battery isolator to keep them both charged. Here is an article on the isolator: http://www.bluewatermarinesvc.com/html/bat_isolator.html (you can get them from iboats). Add a battery switch and you can use your deep cycle for starting in an emergency. The whole setup including the batteries will probably cost less than a tank of gas this summer :facepalm:.
 

90stingray

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Re: Can I use a car battery for my mercruiser?

^^^^ that's what I would do if I was running a large stereo. Maybe even have a switch to shutoff the subs if you are going to run it even longer.
 

Don S

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Re: Can I use a car battery for my mercruiser?

Would you like to just go down to your boat, turn the battery switch to on. Head to your favorite anchorage, turn on the stereo, maybe some lights and run them all day and night without worrying about discharging the starting battery? Yet when you start your engine, the house battery gets re-charged automatically? Without ever touching the battery switch. never trying to remember to switch from 1 to 2 or both to 1 or is that 2. and still being able to use the house battery as a backup if needed?

Click here
 

Nehalennia

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Re: Can I use a car battery for my mercruiser?

Thank for the replies. I think I will go with a deep cycle marine battery since I power an audio system with amp, sub, and tower speakers, and often keep it on for sustained periods while we are swimming.

Do you have a battery switch? Many will use a starting battery on #1 and a deep cycle on #2. This way you can have the best of both worlds. I have always just used Deep cycles and they have done me just fine. With a well tuned engine that starts as it should, the CCA should not matter as much.
 

mjgates

Petty Officer 3rd Class
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May 5, 2010
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Re: Can I use a car battery for my mercruiser?

With all of that stuff you might be better off adding a second battery for your accessories. The deep cycle battery is not designed to deliver high cranking amps for starting, and after a few hours of running accessories might not be able to deliver what you need to start. A reasonable solution is to have a good high cranking amp starting battery wired to the starter (auto should be OK) and a second deep cycle battery to run the accessories, along with a battery isolator to keep them both charged. Here is an article on the isolator: http://www.bluewatermarinesvc.com/html/bat_isolator.html (you can get them from iboats). Add a battery switch and you can use your deep cycle for starting in an emergency. The whole setup including the batteries will probably cost less than a tank of gas this summer :facepalm:.

I see several from iboats, ranging in price from almost $70 and up. Some show an amp configuration, not sure what I would need in those regards. Then some don't such as this one http://www.iboats.com/Marine-Battery-Isolator-1-Alternator-2-Batteries-ProMariner/dm/*******.685394719--**********.852708067--view_id.237463 Would this be suffice for what I run at $70, or should I get one with an amp configuration. This does not appear to use a switch, which I like from Don S post.
 

stonyloam

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Re: Can I use a car battery for my mercruiser?

I think the AMP they refer to is charging AMPeres from the alternator, the one that you linked to should be fine. You don't really need the switch, but it would be useful in an emergency to boost your starter battery if you need it. Here is a simple diagram: http://www.boatfix.com/how/Ele2.html The battery switch in your case would only be used to connect either, or both batteries to the starter. Should have 4 positions on switch off, 1, 2 and all. Your electronics and lights would be wired directly (not through switch)to bat 2 (deep cycle). With the isolator, your alternator should keep everything charged.
 
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