Small outboard starter battery: Deep Discharge or Dual Purpose? - SailNet Community
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post #1 of 13 Old 03-28-2016 Thread Starter
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Small outboard starter battery: Deep Discharge or Dual Purpose?

My battery failed yesterday. I had kept it at 12.8-12.9 volts all winter, but after topping off for a few hours over the weekend, voltage suddenly dropped to about 11. I brought it home, topped off the water (which wasn't terribly low), and charged overnight in my garage, but still just 11 volts. I think one of the cells has failed.

I need to think about a replacement. This battery is a dual purpose battery that I had originally bought as a starter battery for my 50 hp motorboat. Shortly after buying it I re-purposed it for Take Five. So I am confronted with the decision whether to buy another dual purpose, or go with a deep cycle battery instead.

I've read multiple places that the starter motors for 8-10 hp outboards can run off of deep cycle because they don't draw that many cranking amps, but I've never personally tested this hypothesis.

What experience do all of you have with deep cycle batteries doubling as starter batteries for these small outboards?


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PO of 1998 Catalina 250WK Take Five (new owners relocated to Baltimore's Inner Harbor)
1991 15' Trophy (Lake Wallenpaupack)
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post #2 of 13 Old 03-28-2016 Thread Starter
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Re: Small outboard starter battery: Deep Discharge or Dual Purpose?

I guess my question is complicated somewhat by the rumors that I have heard that many battery retailers (Walmart, Interstate?) have started labeling their dual purpose batteries as deep cycle. So my follow-up question would be how to tell whether someone is selling me a true deep cycle battery, as opposed to a dual purpose one that's just labeled as deep cycle?


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2001 Catalina 34MkII Breakin' Away (at Rock Hall Landing Marina)
PO of 1998 Catalina 250WK Take Five (new owners relocated to Baltimore's Inner Harbor)
1991 15' Trophy (Lake Wallenpaupack)
1985 14' Phantom (Lake Wallenpaupack)
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post #3 of 13 Old 03-28-2016
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Re: Small outboard starter battery: Deep Discharge or Dual Purpose?

Maine will probably chime in shortly, but here is how I explain it;

Flooded Lead Acid batteries span a spectrum from: Deep Cycle aka Deep Discharge which have thick lead antimony plates and heavier cases for more charge/discharge cycles, to Starting aka Automotive which have thinner plates and lighter cases to save weight and thereby improve fuel economy.

Because there is NO LEGAL STANDARD as to what constitutes a "Deep Cyle," a "Marine" or a "Start" battery, many companies take a "Marine" label and slap it on a starting battery, and charge a "marine" premium price for it.


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post #4 of 13 Old 03-28-2016
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Re: Small outboard starter battery: Deep Discharge or Dual Purpose?

I assume you are looking at something like a Group 24 or 27 battery. For your application, I don't think it makes much difference if you buy a "deep cycle" or "dual purpose" battery. Generally the ones marketed as deep cycle are rated for a few less cranking amps, but still plenty to start an outboard. You'll pay a bit more for the deep cycle, but it will probably last longer, assuming proper charging and maintenance.
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post #5 of 13 Old 03-28-2016
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Re: Small outboard starter battery: Deep Discharge or Dual Purpose?

Yes, I have been reading a lot about batteries lately, and apparently one way to tell is to simply pick it up. If it is not much heavier than a "standard starting battery" then it is likely not good. Not sure how exactly you use this boat, as I know you cruse on a friends boat, but if you plan on more than just a weekend or two a season (assuming it is the only battery on your boat) I would look at a real deep cycle battery. Not only will it last longer per charge, it will last for more charges. I guess it also depends on how you are going to be charging(just using alternator on the outboard, or shore power, or solar. One nice thing about an outboard is if the battery gets too low to crank you can just pull start it, assuming it has a pull start rope on it. My plan for a budget battery is to use 2 6 volt golf cart batteries, but I doubt you really have the space for that on your boat.

On the other hand I believe Alex from Jiulietta(of Anything-sailing.com fame) just uses a standard auto starting battery or two, just because they are lighter weight and plans on replacing them every second year. Miss him around here, hope he comes back.

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post #6 of 13 Old 03-29-2016 Thread Starter
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Re: Small outboard starter battery: Deep Discharge or Dual Purpose?

The friend's boat was just for last summer - not sure yet about this year. And even with access to that boat from Jun-Aug, we did cruise our own boat for a couple weeks last year in May and September. We expect to do at least the same amount this year (though also chartering in May). My old batteries are identical Walmart Dual Purpose 24DP batteries (purchased before I knew to avoid Walmart batteries). But they're no longer identical, since one has failed. It looks like I caught it soon enough to save the second battery, but now I have an "orphan" that I'd be reluctant to pair with a new battery.

I do have limited horizontal clearance, so I can't really go with anything larger than Group 24. And limited vertical clearance prevents golf cart batteries. But I do have spots for two Group 24s wired in parallel. I am sure that I could make it though a cruise with only one of them, especially since I do have the pull start option if the one discharges. But I like that idea of two batteries in parallel because I think it will prolong their life by cutting the amount of discharge in half. We're very thrifty with power, never dropping below 12.4 with our previous two Group 24s (connected in parallel) even under load. But one did fail after less than 4 seasons, so that's a little disappointing. We have shore power to charge them up, and it's possible the charger contributed to the failure.

I called a couple dealers today looking for US Battery Group 24DC, but both told me that very few companies make the 24DC models. Both told me that US Battery does not make a DC battery smaller than Group 27. When I told them that they show a 24DC on their website, they claimed that USBattery just relabels Crown's 24DC model. One of them tried to sell me a Deka 24DC for $100, and the other tried to sell me Exide 24DC for $90. Neither of these is on MaineSail's top tier list, but his list is not specific to Group 24.


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Re: Small outboard starter battery: Deep Discharge or Dual Purpose?

If I were you, I would just go with the Exide or Deka. Either should work fine for your application. If you really want true deep cycles, then see if two golf cart batteries will fit.
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post #8 of 13 Old 03-29-2016
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Re: Small outboard starter battery: Deep Discharge or Dual Purpose?

My last dinghy had an electric start for an 18hp tohatsu. The start battery died and I decided to eliminate the weight and ditch the battery. After a few months, I actually missed the electric start, but didn't want to spend the $100+ on a massively heavy marine start battery. So I took a chance and bought a little maintenance free flooded lawn tractor start battery. Sacrilege for marine usage but it was very small, maybe a tad bigger than a motorcycle start battery (which may also work), and was only $40. It lasted 3 years, charging off nothing but the weekend use of the dingy and a trickle charger over the winter, not unlike its marine counterpart. So, I tossed it and bought another. It was lighter and cheaper and I was ahead of the game. Hard to get a long life off a start battery that isn't charged frequently anyway, but a trickle charger during the season would have undoubtedly extended its lifespan. YMMV.
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post #9 of 13 Old 03-29-2016
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Re: Small outboard starter battery: Deep Discharge or Dual Purpose?

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Originally Posted by TakeFive View Post


I called a couple dealers today looking for US Battery Group 24DC, but both told me that very few companies make the 24DC models. Both told me that US Battery does not make a DC battery smaller than Group 27. When I told them that they show a 24DC on their website, they claimed that USBattery just relabels Crown's 24DC model. One of them tried to sell me a Deka 24DC for $100, and the other tried to sell me Exide 24DC for $90. Neither of these is on MaineSail's top tier list, but his list is not specific to Group 24.
If you are dealing with flooded batteries NO ONE makes a true "deep cycle" battery though many do "market" them as deep cycle... They are DISO's deep-cycle in sticker only....

That said I do believe the US Battery DC-XC2 line and the Trojan SCS line are about the best of the flooded Group 24, 27 & 31's out there. Still despite the marketing rubbish these batteries do not cycle nor last as long as a golf cart battery or other flooded deep cycle product that was designed from the ground up as a deep cycle product.

You can find deep-cycle GEL & AGM in G-24, 27 & 31 cases but in flooded batteries they are simply misleading you about cycling capabilities..

Can they work? Absolutely but don't pay a "premium" becuase you think you're getting a deep-cycle product. Just buy what fits and replace it when it dies or modify the boat to accept a 12V or 6V bank of golf cart batteries....

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post #10 of 13 Old 03-29-2016
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Re: Small outboard starter battery: Deep Discharge or Dual Purpose?

I have one battery on my Oday 23 that I use to both start my 8 hp outboard (two stroke) and as the house battery. As the house battery, the battery is rarely used for anything other than running the chart plotter/depth sounder for daysails. The outboard has an alternator, but I have no idea how efficient it is. Regardless, the outboard rarely runs for more than an hour a daysail. I take the battery home for the winter and fully charge it a few times over the off-season before reinstalling it in the spring.

I have alternated between deep cycle batteries and the dual mode batteries over the years. My thinking has always been that the starting load for the small outboard wasn't enough reason to justify buying the dual mode battery. When my last battery bit the dust three or four years ago, West Marine was having a sale, so I bought one of those dual mode batteries. It still fully charges (at least it did a month ago when I hooked it up again), and I am curious to see if it lasts all season again. Plenty of juice to start the outboard, and no problem running the chart plotter, the VHF, and the occasional nav and interior lights.
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