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Battery replacement

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sailboat
Navigator

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USA
149 Posts

Initially Posted - 02/04/2018 : 16:45:12

Our 1981 SR/SK has one group 27 battery but thinking of replacing that with two deep cycle group 24s rather than two 27s due to space limitations. Also intend to install a two bank battery charger and battery switch. The electrical load consists of cabin lights (all LED), chart plotter, depth sounder, VHF radio, and a small stereo with two speakers. The engine is manual start and has a 5 amp charging unit with it. With that said do you folks see any great disadvantage for going with the 24 vice the 27.

Thanks.

Mike
Chariots of Fire
1981 Cat-25. sail number 2230
SR/SK Dinette Version

Dave5041
Former Mainsheet Editor

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USA
3754 Posts

Response Posted - 02/04/2018 : 17:02:25

Its all a matter of demand, and yours seems pretty light. I sometimes spend some nights on the hook and have 2 X 27 that fit in the battery compartment with a traditional interior. I also use a a single bank charger connected through the battery switch. It would take a while if both batteries were 50% discharged, but my demand is also pretty low except for running and charging a laptop and has never been an issue.

Dave B. aboard Pearl
1982 TR/SK/Trad. #3399
Lake Erie/Florida Panhandle

sethp001
Mainsheet C-25 Tech Editor

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814 Posts

Response Posted - 02/04/2018 : 23:00:26

I fit two Group 29/31 batteries in the battery compartment on our '87. If you use your stereo, that will be your biggest power draw. Theoretically you don't need two batteries because you have a pull-start motor with a generator. If your battery was low on charge or failed, you could run the motor to power lights, charts, and VHF if necessary. That being said, extra battery capacity is always nice.

Is the generator on your motor voltage regulated?

Seth
"Outlier" 1987 Catalina 25 SR/SK/Traditional Interior #5541
"Zoo" 1977 Morgan Out Island 30
"Nomad" 1980 Prindle 16
"Lost" 1988 Catalina Capri 14.2 (sold - yay!)
"Marine Tex 1" Unknown Origin POS 8' Fiberglass Dinghy
https://whichsailboat.com/2014/07/27/catalina-25-review/

islander
Master Marine Consultant

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USA
3992 Posts

Response Posted - 02/05/2018 : 10:18:39

This is a hard question to answer because we don't know how you plan to use the boat. A week long trip or just an overnight. When it comes to batteries it's all about Amp hours and how many you have to run your electrical needs. You have to add up those needs to see what you will typically use in a 24hr. period. Each item usually has its power consumption printed on it or in its literature stated in Watts or Amps and will be what it uses per hour. Then figure out how many hours a day you will use each item. When you get the total amps that you will be using in 24hr's, Subtract that from your total amp hours you have in your batteries. Two group 24's wired in parallel will give you @160 amp hrs at 12volts. You could use the engine as a charger but it probably produces the 5 Amps per hour at high RPM so it might be a little noisy.
To convert Watts to Amps
Watts/Volts=Amps
Some common battery size codes used are: (ratings are approximate)

Group 24 70-85 Amp hours 12 volts
Group 27 85-105 Amp hours 12 volts
Group 31 95-125 Amp hours 12 volts

Scott-"IMPULSE"87'C25/SR/WK/Din.#5688
Sailing out of Glen Cove,L.I Sound

Edited by - islander on 02/05/2018 10:21:05

Stinkpotter
Master Marine Consultant

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Djibouti
9013 Posts

Response Posted - 02/05/2018 : 16:58:26

The key advantage to two smaller (24s) with a selector switch over one larger is insurance. If you use just one of the two for your house duties and it becomes perilously low, you have the other, which for some can be critical. I have two group-24s and use just one on the hook, which insures I can start my outboard. (Since it's a 3.5L V-6, that would be a little more difficult to do with a pull-starter than yours.) The advantage of one larger battery is simplicity. You don't seem to have any super-critical uses, so amp-hours are your factor.

Dave Bristle
Association "Port Captain" for Mystic/Stonington CT
PO of 1985 C-25 SR/FK #5032 Passage, USCG "sixpack" (expired),
Now on Eastern 27 $+!nkp*+ Sarge

Dave5041
Former Mainsheet Editor

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USA
3754 Posts

Response Posted - 02/05/2018 : 18:00:32

Also, you should consider only half the the battery's capacity available. Batteries should be discharged to 75% of capacity periodically, but discharging below 50% will shorten battery life Never discharging below 90% will also shorten a battery's life..

Dave B. aboard Pearl
1982 TR/SK/Trad. #3399
Lake Erie/Florida Panhandle

Stinkpotter
Master Marine Consultant

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Djibouti
9013 Posts

Response Posted - 02/05/2018 : 19:34:46

quote:
Originally posted by Dave5041

...Never discharging below 90% will also shorten a battery's life.

I've only heard that regarding NiCad batteries--never lead-acid. I suspect my car batteries have almost never gone below 90%, and they typically last me 8+ years.

Dave Bristle
Association "Port Captain" for Mystic/Stonington CT
PO of 1985 C-25 SR/FK #5032 Passage, USCG "sixpack" (expired),
Now on Eastern 27 $+!nkp*+ Sarge

Edited by - Stinkpotter on 02/05/2018 19:38:02

OLarryR
Master Marine Consultant

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USA
3367 Posts

Response Posted - 02/06/2018 : 04:28:12

My batteries never get seriously discharged since I use a 20 watt solar panel to charge the banks. The original batteries held their charge until I replaced them at 7+ years or so use. (PO had them for at least a year before I purchased the boat.)Even then, they probably could have gone an addl year or more. I only replaced them because I had bought an AGM battery from the marine store as a battery backup for my sump pump at home - A hurricane was coming our way. But the hurricane passed with no ill effects and since I then had an unused AGM, I decided to buy another and replace my boat batteries.

I also have a charger for independently charging each battery but I only use the charger when staying overnight at a marina and wind up running my cabin lights and mini-boombox for an extended period of time. These overnighters have been rare and so it is my 20 watt solar panel that keeps the batteries fully charged year-round. My marina would be charging me about $20/month for m size boat if I utilized dockside power...which I do not.

Larry
'89 Robin's Nest#5820, Potomac River/Quantico, Va
http://catalina25.homestead.com/olarryr.html

sailboat
Navigator

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USA
149 Posts

Response Posted - 02/06/2018 : 16:53:13

The use of the boat is day sailing and occasional overnighters.

Mike
Chariots of Fire
1981 Cat-25. sail number 2230
SR/SK Dinette Version

Stinkpotter
Master Marine Consultant

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Djibouti
9013 Posts

Response Posted - 02/06/2018 : 20:16:44

K.I.S.S.

Dave Bristle
Association "Port Captain" for Mystic/Stonington CT
PO of 1985 C-25 SR/FK #5032 Passage, USCG "sixpack" (expired),
Now on Eastern 27 $+!nkp*+ Sarge

Dave5041
Former Mainsheet Editor

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USA
3754 Posts

Response Posted - 02/06/2018 : 20:24:15

I came across the periodic discharge rule on multiple battery manufacturers sites when I was researching batteries for my last replacement cycle. Car batteries are designed for short, high current drains and immediate recharge and staying in a fully charged state and are designed to perform within those parameters. In addition to the physical differences in the plates, different metals alloyed with the lead can impact the electrical performance and chemical stability of the battery. I don't see a financial advantage in the information for manufacturers so I adhere to the suggestion.

Dave B. aboard Pearl
1982 TR/SK/Trad. #3399
Lake Erie/Florida Panhandle

Dave5041
Former Mainsheet Editor

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USA
3754 Posts

Response Posted - 02/06/2018 : 21:37:19

Some additional research suggests a possible reason for the recommendation for moderate discharge cycling. Deep cycle batteries need to be cycled 50-100 times before they reach full capacity. In many applications this might not happen before the battery power is needed. The contraction and expansion of the plates during discharging and charging moves the electrolyte deeper into the plates, taking the battery from an initial capacity of about 85% of rated capacity to about 100%. Incidentally, a car battery can fall to 30-40% of rated capacity before a sudden cold snap tells you that your battery just died It was actually in hospice care for a long time before that happened. Our deep cycle batteries get noticed long before that.

Dave B. aboard Pearl
1982 TR/SK/Trad. #3399
Lake Erie/Florida Panhandle

RichardG
Admiral

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USA
990 Posts

Response Posted - 02/08/2018 : 16:35:14

When my kids were younger, and watching lots of Disney videos, running lights, playing music, etc. for days on end, it seemed like I would go through 24s or 27s for breakfast. About 10 years ago I got two 6 volt golf cart batteries from Costco, and wired them in series. This worked much, much better. That set lasted many years under severe abuse, and I replaced it with a new set last year. I typically go out cruising on 3-5 day trips, with no re-charging until back at the slip. I guess I consider electricity the same as gasoline on my boat - I bring all that I may need.

RichardG 81 FK/SR #2657
Terminal Island, CA

Sailynn
Navigator

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USA
178 Posts

Response Posted - 02/08/2018 : 19:01:04

We have one group 27, all LED, knot/depth finder, handheld VHF, battery operated speaker and I-pod, a new 20 watt solar charger on the stern pulpit, shore power and 9.8 Tohatsu with electric start and charger. Haven't used shore power for two years. Do 1-2 overnighters most the time.

Lynn Buchanan
1988 C25 SR/WK #5777
Sailynn
Nevada City, CA

Akenumber
Navigator

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USA
247 Posts

Response Posted - 03/01/2018 : 18:36:15

I have two 31's and they last for days with stereo lights and ARB fridge. I do not need more bank, due to the fact that on a mooring I can't charge much more bank. All in all pretty happy.

Ken
San Diego
84 C25 SR/FK 4116
The KRAKEN

WesAllen
Navigator

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USA
222 Posts

Response Posted - 03/01/2018 : 22:15:13

I have 2 group 31 AGM batteries (105 amps each) and have gone 3 days with out a charger using my CPAP machine, stereo, VHF, Chart plotter, etc. with no problems. I am very happy that I went to that size. They barely fit in the starboard battery compartment thou. Plus my Merc charges when running. 2 batteries are certainly better (my experience only, for peace of my mind which is pretty small

Wesley Allen
"Breaking Wind"
1982 C-25 SR/TR/SK #2773
Hemlock, MI

Voyager
Master Marine Consultant

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USA
5231 Posts

Response Posted - 03/02/2018 : 19:38:19

Has anybody successfully used a cold plate on their boats? Coleman makes a gizmo you can put inside a cooler and plug it into a 12V source at 4A and it will cool down to 40�F below ambient temperature. At 80� that�s 40� so it might keep your ice for longer than normal. But at 4A you can kill your group 24 in about 10 hours and a group 27 in about 11-12 hours.
Another approach is to use a 3-day cooler with better insulation.
But I�ve seen them in truckstops. Anybody use one?

Bruce Ross
Passage ~ SR-FK ~ C25 #5032

Port Captain � Milford, CT

Stinkpotter
Master Marine Consultant

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Djibouti
9013 Posts

Response Posted - 03/02/2018 : 20:47:04

I froze jugs of water at home, let them slowly melt in the cooler as they refrigerated everything else, and used the resulting water for drinking. Worked for days.

Dave Bristle
Association "Port Captain" for Mystic/Stonington CT
PO of 1985 C-25 SR/FK #5032 Passage, USCG "sixpack" (expired),
Now on Eastern 27 $+!nkp*+ Sarge

Edited by - Stinkpotter on 03/02/2018 20:47:45

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