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chartscharts 11-18-2012 06:16 PM

Battery Sizing - am I crazy?

My CAL29 is in need of new batteries. The existing ones are shot and won't hold a charge. I wanted to solicit opinions about downsizing drastically.

My existing batteries are a bank of two of these: Trojan EV8D, 12Volt, 220AH@20hr, batteries. They are big and weigh a gazillion pounds a piece. More than I can easily remove myself, a big disadvantage.

My needs are modest. It primarily needs to start my Farymann A30, single cylinder, 10HP diesel. I have the usual running lights and house lights and VHF radio.

My sailing habits are almost exclusively day sailing. 2-3 times a year (on good years) I'll take it out for an overnight. I could use battery powered camping lanterns on those even, since it's not very often.

So I think I might be able to drastically downsize, allowing for easier and cheaper maintenance and replacement. Going to something like two of these:

EverStart Group Size 29DC Marine Battery: Automotive :

Am I crazy? What am I not thinking of?


Minnewaska 11-18-2012 06:38 PM

Re: Battery Sizing - am I crazy?
Those are big dogs at 155 lbs a piece. No shame in not wanting to haul those in and out.

If you can size a smaller battery at 2x your normal usage, then go for it. You could always replace the 8D with two smaller batts that are connected in parallel.

blt2ski 11-18-2012 07:09 PM

Re: Battery Sizing - am I crazy?
You need to do something like I have in my 30' boat. I have a typical size 24 starting battery for my 2 cy Yanmar, then a separate house battery that is a true deep cycle battery. They should not be run together for house lighting etc needs. You might find depending upon useage, a size 24, 27 or 31 12V lead DCycle batter will work for your needs. If you are going say a week at a time, then yes, keep the 2 8D's if that is what you have. Reality is, my setup will work for what you have. I did have a size 24 for the house, recently put in a 31 for a few more AHrs to work with.


asdf38 11-18-2012 07:18 PM

Re: Battery Sizing - am I crazy?
It's hard to argue with simplicity. It looks like you chose a deep cycle which in my opinion would be the best thing to do if you're going with one battery. Deep cycles still have plenty of cranking power and you're one cylinder isn't going to draw a ton.

However I don't know that particular battery and the usual battery purchasing cautions apply: if you want a deep cycle, make sure it's really a deep cycle. Deep cycles will always have the 20 hour Ah rate marked on them. That said I know plenty of people around here go with Wal-Mart. If you have a Sam's Club nearby also consider this:

But also consider that you'll have no reserve bank should you leave a cabin light on and drain your one battery. Then you'll be stuck. One thing I considered with my 1 cylinder Yanmar was using a small $35 tractor battery as a reserve/start instead of a standard marine size one. You could consider that too if you wanted the usual reserve bank functionality but without much cost or weight.

Waltthesalt 11-18-2012 07:41 PM

Re: Battery Sizing - am I crazy?
I agree with what's been said and your plan. If you're not going to do any rewiring then you want both the batteries to be the same type and age so that you charge them in parallel. It appears that someone wanted to have the battery bank be a larger capacity than needed for engine starting and light loading. The current, and more practical, thought to address this is to have a bigger deep cycle type battery for the hotel loads and a smaller starting battery that's spec'd to your engine requirements. with this type of arrangement however you'll need a different battery distribution panel which one battery is for the engine and the other for hotel loads, with a cross connect feature. You'll also need a charging circuit that uses a VSR relay or duo type charge that allows for the fact that the different batteries charge at differrent times and rates.

chucklesR 11-19-2012 09:32 AM

Re: Battery Sizing - am I crazy?
Somebody sold the previous owner a massive bank or batteries, or his usage was much different that yours.

Your plan is fine for your intended usage. Good luck getting the old ones out, use the boom as a lifting arm :) and wear something you don't like, or a plastic suit over it.

Siamese 11-19-2012 09:44 AM

Re: Battery Sizing - am I crazy?
I would not use the battery that you linked to at Walmart. Not sure if it's a true deep cycle, and I would DEFINITELY not buy a maintenance free battery for a boat.

Get a deep cycle 12v battery, that you can maintain. Without going into the mechanics of how they achieve "maintenance free" status, I will keep this brief and tell you it's not what you want.

I would typically suggest a bank of two 6v golf cart batteries and a 12v starting battery for emergencies, but for the needs you stated, a conventional lead acid deep cycle battery will serve you well. Keep some distilled water on board and top off the battery regularly.

MedSailor 11-19-2012 02:02 PM

Re: Battery Sizing - am I crazy?

Originally Posted by chartscharts (Post 950150)

My sailing habits are almost exclusively day sailing. 2-3 times a year (on good years) I'll take it out for an overnight.

Ummm.... I don't think you have too much battery capacity, I think you're just not sailing enough! Sail more and stay out longer and then you'll need the batteries! ;)

Drastically downsizing your bank sounds like a very good idea. Just make sure to have 2 separate batteries: one starter style and one deep cycle. I think just about any size and brand would work from group 24 up based on your modest needs.


hellosailor 11-19-2012 02:16 PM

Re: Battery Sizing - am I crazy?
440AH of batteries for mostly daytripping?

You're not crazy. Get two 29D's, leave the battery switch on 'both' most of the time. When you drop the hook and there's a chance you might dawdle and run a battery down, then split the batteries, so you know you'll have one left for starting. No big deal and simplicity pretty much trumps all the theories and options.

In fact, for your use? One 29D or one 31 would probably suffice. Add a "battery brain" or other low-voltage cut-out on the positive post, and that will cut off all loads when you reach a low voltage, saving just enough battery so you can start the engine back up again. No master switch required, just reset it if you pull the battery down that low.

Barquito 11-19-2012 02:32 PM

Re: Battery Sizing - am I crazy?
I'm guessing you can exchange those huge batteries for a little cabbage($$).

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