Series, parallel, or 1 large battery?

   / Series, parallel, or 1 large battery? #1  

EricG1793

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We have a John Deere 310 that currently has a pair of 12-year-old John Deere TY21737 batteries (Interstate equivalent 3EH-VHD). Each battery is 6v, 850cca, reserve of 270 mins. They are in series for 12v. My dad never maintained the batteries and it started cranking weakly in the last couple years, then not at all. He refilled the cells earlier this year and charged the batteries, but they didn't come back.

I tried charging them in series with a 12v Battery Minder 1500 (1.5 amps) but it kept saying the batteries timed out -- probably too much battery for it. I figured the desulfation would be a benefit. Then I took the weaker battery (6.15v; stronger one was 6.25v) and put it on the big charger, which only has a 40 amp setting for 6v. I charged it for 45 minutes or so and it didn't seem to hold a charge. I might have done it for another half hour at some point, still no more charge. So I charged it for 2 hours this morning. Now, it's measuring 4.1 volts... I think I fried a cell, unless I was hallucinating and it was saying 4.1 volts all along. Could the 40 amps at 6v have killed it? That seems like a reasonable current to me, since it's 6v and they're such large batteries, but some of you would probably know better!

Assuming I'll have to replace them (they're definitely old enough), what's the best way to do so? Same setup, about $270? Or perhaps similarly-sized dual 12v batteries such as Interstate 3ET-VHD in parallel, about the same price? Or, one large 12v battery, such as a 4DLT-VHD ($180)?

I'm leaning towards one large battery. Much cheaper, and simpler less terminals to corrode and connect. Just even bigger of a pain to drop way down in that little battery box.... Either that or two 12v in parallel, which would be easier to handle and maintain, since each battery could be charged individually. My understanding is that it would be less stress (amperage) on individual batteries in parallel rather than in series which would theoretically give them an easier life. I know that equalization is an issue with series, perhaps not with parallel? I can't see the benefit in another 6v series set up. Perhaps, in the 70's, that was the most economical setup for the machine?

Thanks for your words of wisdom! :)
 
   / Series, parallel, or 1 large battery? #2  

Gale Hawkins

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Ours came with just on big (not large like to the 265 MF) so I just bought another the same size but not JD brand like the old one. There is room for another 12v but we do not use it below freezing and it starts in a flash at 40F and above. It sometimes sets for a few months but still starts fine.
 
   / Series, parallel, or 1 large battery? #3  

aczlan

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All other things being equal, one large battery will last longer than two smaller ones... The weaker battery in a series or parallel will always make the stronger one work harder.

Aaron Z
 
   / Series, parallel, or 1 large battery? #4  

SPYDERLK

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One big battery. Cheaper than the series setup and less connections as you say. Avoid a parallel setup because when 1 battery weakens the strong battery will charge it while parked and the pair will slowly go dead.
larry
 
   / Series, parallel, or 1 large battery? #5  

Bigfoot62

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Just make sure that you have ENOUGH battery, if you're only going to use one.
I know several people that have burned up a starter on older Ford tractors that were supposed to have a 4DLT, but were replaced with a smaller capacity "car" battery to save money. A new 4DLT is less than $200, a rebuilt starter is over $300. Do the math.
 
   / Series, parallel, or 1 large battery?
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EricG1793

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Thanks for the info, guys!

Bigfoot, that's something I've been briefly tempted by -- getting a high-amperage battery with less reserve. But that's a good point about starters. An extra $50 once every decade (as in our case) isn't much of a sacrifice to have something perform well. The 4DLT I'm talking about is 850cca with a 250 min reserve. Originals are 850cca and 270 min reserve. It always starts in just a couple seconds of cranking, but God forbid something happens to the fuel system and it needs to be primed.

My dad said we'd be stupid to get the big one, since we struggled so much just to get the small ones out (he's 60 and I'm scrawny LOL). I'd like to figure out a way, devise some sort of crane or pulley system.... At least wrap a pair of straps or something around it so we could each grab an end and be able to stand up while lowering it down into the box. It's awkward getting the batteries up in to the cab, then down where they are over a foot below the floor. Too bad we don't have an engine lift. :D But now I'm convinced that it's worth the initial hassle.
 
   / Series, parallel, or 1 large battery? #8  

Big Barn

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   / Series, parallel, or 1 large battery? #9  

orezok

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All other things being equal, one large battery will last longer than two smaller ones... The weaker battery in a series or parallel will always make the stronger one work harder.

Aaron Z

This is true for parallel connections but not series. After all, a 12v battery is six 2v batteries in series. Thats how it works.
 
   / Series, parallel, or 1 large battery? #10  

Gary Fowler

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This is true for parallel connections but not series. After all, a 12v battery is six 2v batteries in series. Thats how it works.
And that is why when one cell goes bad, the battery is dead.
 
 
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