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4d size battery OVERKILL?

Old 10-19-2011, 01:34 PM
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Default 4d size battery OVERKILL?

I have the opportunity to purchase 4d size batteries at a ridicuous price. and I'm currently using 5 batteries in total to run my systems. 2 for house one for each engine and one for the genset. I wonder if gettting two of the 4d's in place of the 5 would work? one for house and one for everything else..THEY are HUGE aprox. 100 pounds each ...But price is right....i figure 5 at 50 pounds each is 250#'s I'd be dropping 50 pounds. and gaining some serious reserve power..one for starting one for house and set up the switches to run anything from anywhere.

opinions?
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Old 10-19-2011, 01:47 PM
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What size do you have now?
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Old 10-19-2011, 01:55 PM
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Nothing with the the number 4 and the letter D in it is oversized.
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Old 10-19-2011, 01:55 PM
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I used two of them on my boat when I did the restoration. One on each motor with the switches wired for seperate or both. I never had to worry about my boat starting thats for sure. I purchased mine from Napa and got a great price. Yeah, call me crazy but with all the electronics not to mention two 14A Rule pumps I had the potential to put quite a load on them.
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Old 10-19-2011, 02:49 PM
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I have 5 i'm assuming group 27's.
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Old 10-19-2011, 03:09 PM
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There's nothing wrong with using 4D batteries, but do you have room for them and do you have a way to put them in place, check them from time to time, and replace them when the time comes?

It was all I could do to install four 75 lb batteries in my boat. Any more and I would have had to place a call to Hulk Hogan for assistance.
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Old 10-19-2011, 04:38 PM
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4D batteries have roughly twice the amp-hour capacity of standard group 27 batteries. The main claim to fame for 4D's is their starting amps. They are mostly used for starting diesel engines, which require lots more amps to start than gas engines due to the high compression that must be overcome to spin them.

One 4D is equivalent to two standard batteries. But when it fails, you don't have the redundancy that the smaller batteries provide.
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Old 10-19-2011, 06:28 PM
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As for space, yes the way the boat is configured now there are 2 outboard of the port engine and three amidships forward of the bait well hatch between the engines the two to port offset the genset which is off to starboard....i figured they are big enough to start both engines and the genset and in the event of a failure i could go to the alternate and still have enough go to crank either the genset ( with ac battery charger) or either engine. I would be going from 5 to two the batteries are reported to be 20 by 11 by 11
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Old 10-20-2011, 04:16 AM
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4D's are usually 115 lbs each and have the same capacity as two group 27's - so you really will have a little less power assuming what you have is 5 grp 27's. In your application, I'd rather have three banks - one for each engine and one house bank; personally I wouldn't waste my time (or the added weight) with a dedicated generator battery - just put in a 1-2-all switch on your starting batteries for it.
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Old 10-20-2011, 05:35 AM
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Originally Posted by LI32 View Post
I'd rather have three banks - one for each engine and one house bank; just put in a 1-2-all switch on your starting batteries for it.
Maybe I should replace the two house with one 4d and keep the two independant starting batts for each engine and lose the gen battery...I've used the generator twice since i bought the boat and with some creative switch and charging configuration make a setup where any engine could be started from any battery...I've also got to check my charger and see how its configured and its capabilities. Thanks
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Old 10-20-2011, 01:07 PM
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Originally Posted by westiemax View Post
Maybe I should replace the two house with one 4d and keep the two independant starting batts for each engine and lose the gen battery...I've used the generator twice since i bought the boat and with some creative switch and charging configuration make a setup where any engine could be started from any battery...I've also got to check my charger and see how its configured and its capabilities. Thanks
THAT is what I would do.

Here is your creative 3 bank drawing with Geni, using BEP's switch and VSR cluster. My geni is run off the Stbd battery bank. I can parallel just about any combo of the batteries, and they are all always getting charged by the AC charger and off either motor or Geni. Just switch the 2 House batteries in the drawing with 1 4d.


Last edited by Birdman; 10-21-2011 at 09:15 AM.
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Old 10-20-2011, 05:20 PM
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Thanks Bird... you did my homework for me.
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