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Old 09-26-2017, 10:06 AM   #1
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What to do for my lacking dual batteries on a 7.3l?

Hey all, so i am needing to replace my starting batteries on my 1996 7.3l Sportsmobile. I went out and bought 2 new group 65 batteries rated at 850 cca's and figured I would be good to go. Not the case.... I guess when Sportsmobile installed the starcool under my hood they kept the dual battery setup under the hood (yea its tight) but made the passengers side one that is by the starcool smaller.

So I have 1 group 65 with 850cca and 1 measly group 50 with only 600 cca. Obviously this seems less than ideal for a 7.3l but it has been this way for 20 years before I owned it. So my question is where do I go from here, keep it easy and just leave it as is...... or relocate the 2nd one to under the frame?? I know that ideally I would like to have 2 group 65's for the extra cranking amps especially with winter coming up here in SLC Utah. But I also don't really want to spend the extra money or spend the time trying to figure out what parts I need with a frame box, new cable etc (im sure I could do it just never have before so it would take some extra research).

Im not super experienced in this area but my limited knowledge understands that if I have 2 different sized batteries in parallel or however they are wired, will my alternator only charge the bigger battery to the capacity of the smaller group 50? If so I am guessing that isn't the best for clean starts on this beastly 7.3, but again its worked this long so what should I do?
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Old 09-26-2017, 12:07 PM   #2
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Originally Posted by nemesisnight View Post

Im not super experienced in this area but my limited knowledge understands that if I have 2 different sized batteries in parallel or however they are wired, will my alternator only charge the bigger battery to the capacity of the smaller group 50?
Thankfully that's not the case or all of us are wasting $$ on big house batteries. When either the alternator is spinning or the solar is solar-ing my large house batteries and my measly starting battery are connected in parallel by the separator and they all manage to get fully charged.
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Old 09-26-2017, 01:30 PM   #3
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Thankfully that's not the case or all of us are wasting $$ on big house batteries. When either the alternator is spinning or the solar is solar-ing my large house batteries and my measly starting battery are connected in parallel by the separator and they all manage to get fully charged.
Thanks, boywonder that's good to know, I did some random google search and was reading all sorts of weird ideas and it seemed like the 2 different size batteries was not recommended. But I have seen that maybe Ford had done this stock on some of these older vans so maybe I should just keep it easy and replace with the same "mis-sized" batteries that are bad instead of all the rewiring that would be needed for 2 group 65 ones. Unless someone talks me out of it, or has better insight then maybe those extra 250 cca aren't needed (although maybe helpful).
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Old 09-26-2017, 02:25 PM   #4
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Thankfully that's not the case or all of us are wasting $$ on big house batteries. When either the alternator is spinning or the solar is solar-ing my large house batteries and my measly starting battery are connected in parallel by the separator and they all manage to get fully charged.
But on the other hand, your van battery and your house battery are likely separated by either an isolator or a separator. I think the OP's question is about his two van (starting) batteries being different sizes/capacities, which IMO is a whole 'nother animal. I don't think batteries that are directly tied together should be different, but that's more personal preference than anything I've personally researched.

Recommend getting Scalf77 to weigh in on this. He's the van electrical guru.


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Old 09-26-2017, 05:40 PM   #5
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Originally Posted by nemesisnight View Post
Hey all, so i am needing to replace my starting batteries on my 1996 7.3l Sportsmobile. I went out and bought 2 new group 65 batteries rated at 850 cca's and figured I would be good to go. Not the case.... I guess when Sportsmobile installed the starcool under my hood they kept the dual battery setup under the hood (yea its tight) but made the passengers side one that is by the starcool smaller.

So I have 1 group 65 with 850cca and 1 measly group 50 with only 600 cca. ...?
I had the same issue in my '95 7.3L, it turns out it was Ford that did that... I just replaced both of my underhood Batteries, the replacement manual calls for a group 50 (special order at my local Napa AS) on the passenger side. I can't complain, these batteries have been in it since at least 2011. You always want to replace batteries wired in parallel as a pair, so if one bites the dust, you replace both.
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