Danny;
Batteries come in three basic constructions: Starting Batteries: For a given weight of lead (which is what determines the AH capacity of the battery, a heavier battery has greater capacity to store energy than a lighter one) this type of battery uses a larger number of thinner plates. The maximum current provided by the battery is a function of the surface area of the plates in the battery. So a battery with a lot of thin plates results in a lot of Cold Cranking Amps (CCA). But the thin plates tend to be flexible, so unless there is some other structure designed into the battery case, start batteries are sensitive to internal shorts from vibration and shock (think about choppy water or falling off a 5’ wave when offshore). The greater surface area also leads to a higher degree of sulphation and sluffing of surface material during long periods of storage. These are typical car batteries that almost never get below about 95% state of charge and are not subject to shock. Deep Cycle Batteries: Uses a small number of thick plates. Much more resistant to shock and vibration, and are designed to provide current flow at a lower rate over a longer period of time. Dual Purpose (also commonly called Marine Starting) batteries: A compromise between start and deep cycle, typically with some intermediate number of thicker plates to get lower cranking amps but greater resistance to shock, and vibration, and less degradation of the battery during longer periods of inactivity. Generally a good choice for smaller power boats with bigger engines that need a lot of amps to crank over. A note about cranking amps: For a boat, don’t get too focused on CCA. CCA is rated at freezing temperatures; when did you last try to start your boat when it was near zero F or C? And how many cranking amps do you really need? Starting an old big block V8 engine might call for 350 or 400 Amps of current. The installation manual for my 36HP 4 cylinder diesel called for battery cables and fuses to handle a maximum of 175 amps of starting current. YMMV, so look it up for your particular engine. When I worked for the bulldozer company, we had a starting cart with (2) 4D batteries on it, each with something like 1100 CCA. It was not unheard of for an employee to use the cart to jump a car in the cold Illinois winter, and end up burning up the starter or wiring by cranking too long. Also know the Marine Cranking Amp rating (MCA) which is like CCA but at a temperature around 50 F. If your boat has a house bank and a dedicated start battery, the optimum plan is likely deep cycle batteries with maximum AH rating for the house batteries, and a smaller Marine Start battery. Select the start battery to give 50% or 100% more MCA than your engine needs, but much more than that is a waste of size, weight, and money. My boat has (4) group 27 deep cycle house batteries, a total bank of just over 400 AH. My dedicated start battery is also a group 27 deep cycle with a MCA rating of 450 or something like that. When I need to replace the start battery (it was installed in 2007) I’ll go with something like a deep cycle group 24. All my batteries are lead acid. I’m frugal and that gets the best value of life and cost IMHO. The house batteries I replaced last year had been in service for over 8 years. I was product manager for batteries in the aftermarket for both a construction equipment manufacturer and a fork lift manufacturer before I retired. Among other things I learned something that Joe Della Barba alluded to in an earlier post – there are only 3 or 4 battery manufacturers in the US, and they make batteries and label them for many brands. Joe pointed out that DEKA made batteries for West Marine and the Dekka brand cost half as much as the WM brand. I dealt a lot with Globe Battery Division of Johnson Controls. They made Interstate, Napa, Exide, Sears, and many other brands. Sears was an interesting case: every Sears battery of a given BCI was identical electrically, the differences were all in the colors of the plastic case and cover, the cost, and the warranty period. SO the 6 year warranty group 27 Diehard was exactly the same battery as the cheapest group 27 with a 1 year warranty. Personally, since some time in the 90s I’ve bought my deep cycle batteries from Sam’s Club or Walmart – either Exide of Diehard label. The two group 24 deep cycle batteries I recently bought at Walmart of my 25 (replacing batteries with a 2003 warranty sticker) cost about $80. Rick Brass Washington, NC From: CnC-List [mailto:[email protected]] On Behalf Of Danny Haughey via CnC-List Sent: Wednesday, October 17, 2018 9:49 AM To: Francois Rivard via CnC-List <[email protected]> Cc: Danny Haughey <[email protected]> Subject: Re: Stus-List Lithium Batteries LiFe vs Lipo After reading all of this, for my use, the less expensive lead acid batteries seems the right choice and then use the savings for a good solar install (this is really an after the fact justification because I already bought the solar system!). We are weekenders with a week out 2 or 3 times per season. I was wondering what I would do for batteries next time around and this discussion has really helped. My boat has room for 3-group 27 house batteries under the V-Berth and a starting battery under the cockpit. Currently the house batteries are "dual purpose" (whatever that means) 85ah each. I'll go to some good deep cycle batteries next. I think I can get some more amp hours and keep them topped up with a 400watt solar array. My goal is to be able to run the refrigerator and autopilot I'm about to install. I'll keep watching this thread but, if anyone has some advice on a good lead acid deep cycle choice, I'd love to hear it! Danny
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