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Author Topic:   Battery types, which to use
DJS posted 06-30-2002 12:27 PM ET (US)   Profile for DJS   Send Email to DJS  
Lately, it seems that more and more people are recommending using a combination starting/deep cycle battery for starting batteries as well as for trolling use.

Mercury Outboards, on their website says you should use a cranking battery for starting purposes and a deep cycle battery for trolling motors. (Hyperlink)

Can anyone explain how one battery (the combination referred to above) can be sucessfully used for both purposes?

Thanks, David

JBCornwell posted 06-30-2002 01:33 PM ET (US)     Profile for JBCornwell  Send Email to JBCornwell     
Hi, David.

I am one who recommends the "dual purpose" batteries. They have not been in the market very long.

In simplified technical terms, these are deep cycle batteries that have the low internal impedance of a starter battery, thus the ability to supply hundreds of amps on demand, and will tolerate the deep discharging of a troller battery without sulphating the plates.

I have been very happy with the performance of mine.

Red sky at night. . .
JB :)

jimh posted 06-30-2002 04:52 PM ET (US)     Profile for jimh  Send Email to jimh     
(Phew--Had to fix that URI to the Mercury website. The link contained more text than the page it points to! There ought to be a law against that!--jimh.)
RWM posted 06-30-2002 05:58 PM ET (US)     Profile for RWM  Send Email to RWM     
I've used a deep cycle battery as my only battery on a Montauk for years. Why not?
DJS posted 07-01-2002 10:44 AM ET (US)     Profile for DJS  Send Email to DJS     

I'm sorry that you needed to fix the Mercury url. If I was more computer literate I would have done it. I used that site to illustrate what I was referring to. Thanks for you trouble.


Until lately everything I understood about "starting batteries" and "deep cycle batteries" was similar to the information that is provided on the hyperlink shown above. Now it seems that this has changed in actual use. More and more I see people using the "dual purpose" type batteries. As a matter of fact I have two of these dual purpose types in my 1987 22 Outrage at the present time. I just don't understand what has changed to make the dual purpose batteries handle both types of loads. Also, I wonder if the dual purpose batteries are as capable as the single purpose batteries. I am going to be replacing my batteries soon and I wanted information on a subject I do not fully understand.


John W posted 07-01-2002 11:13 AM ET (US)     Profile for John W  Send Email to John W     
The ONLY disadvantage of a deep cycle battery for starting is that they have lower cranking amps than a similar sized cranking battery. In every other way a deep cycle battery is a better battery IMHO & will last longer, even in starting duty. The key is getting a deep cycle battery with enough cranking amps to easily start your motor. There was a time when that might've been hard to find, but not anymore. The only exception is for some of these DFI outboards that require very high amps...then a suitable deep cycle battery with enough cranking amps might be overly large, heavy & expensive.

I've used deep cycle batteries for my starting battery for many years on a variety of boats & motors without problems, and battery life is improved. For the past 4 years I've used AGM type maintenance free deep cycle batteries for starting & backup/deep cycle use & they've been wonderful.

Many people reccommend a starting battery for your motor and a deep cycle battery for your electronics, pumps, etc. But I prefer having one deep cycle battery running everything including starting the engine, and a fully charged, unused battery as a backup. That way, if your starting battery shorts out, you aren't left trying to start your motor with a deep cycle battery that has been drained down from a day's use on baitwell pumps etc. If my main battey goes out, I have a fully charged identical backup. But this setup only works if your starting battery is a deep cycle that can handle being drained by pumps & electronics.

Jim Bennett posted 07-02-2002 08:06 AM ET (US)     Profile for Jim Bennett  Send Email to Jim Bennett     
Have checked this thread and others but will like a little more feedback. My restoration project of a 73 OR 21 is at the reassembly stage and am about to get new battery. First thought I would use 2-battery setup in console but have decided on single at starboard rear as in original. Purchased West Marine group 27 combo battery last summer just to tryout engine. Recently purchased Boston Whaler flat top tan battery box from Sue at Twin Cities. Box however is for group 24 battery. Will keep 27 as spare but would like to have opinions on battery brand. Should I get a combo 24 from West or another brand? I believe several have advised previously about AC Delco Marine batteries. Additional feedback would be appreciated.
goldstem posted 07-02-2002 12:06 PM ET (US)     Profile for goldstem  Send Email to goldstem     
I have been very happy with an AC delco group 24 battery. have had it for 6 years now! Every spring I think I'll need a new one and it keeps plugging along.
BTW, in my 1972 outrage 21, the battery is on the port side, not starboard! I think that was to offset some weight of the kicker motor (which I sold years ago, as I can't get the old 140 1981 evinrude to fail!)
nutah posted 07-04-2002 04:09 PM ET (US)     Profile for nutah  Send Email to nutah     
I am considering relocating my dual purpose batteries from the stern to the center console in my Montauk 17, to change trim and clear deck. Had a battery that was being charged explode in the engine compartment of a boat when a crew member pulled the charger cable off the battery while the charger was still on. Explosive gas plus sparks is BAD!
No fire, just blew top of battery and spewed hot acid all over everything and me. I have seen batteries mounted in the CC on Whalers. The CC is vented and there shouldn't be sparks; a better situation than most IO engine boxes, but no blower. I would appreciate any feedback. I love this forum, it is a treasure chest of information. Thanks to all who have contributed and to the guys that set this up.

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