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Old 03-26-2015, 05:29 PM   #1
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I know the answer but gotta ask...

I have a Deka DP24 (dual-purpose marine battery) that's in good shape and less than a year old. It's my only battery. I'm prepping for dry camping and need more.

I can get a DC27 for $95 plus core. I need 2. Counting a new (cheap) box, core charge and tax, that's $255 for a pair.

I'm already spending hundreds of dollars in prep for my trip. If I can use the DP24 in parallel with 1 DC27, I'll save some much-needed dough.

I've read recommendations that batteries should be the same brand, type, size and age, for maximum efficiency, and don't dispute that. But, if I make this trip with 1 DC27 in parallel with 1 DP24, will that damage either battery?

No stone-throwing, please.
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Old 03-26-2015, 05:39 PM   #2
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Before I paralleled the 2 of them, I'd add a battery switch that lets you pick one and then the other and manage my power usage that way.

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Old 03-26-2015, 05:53 PM   #3
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Hmm... That might work. I hadn't thought of that approach. Good ideas like that is exactly why I posed the question.

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Old 03-26-2015, 06:04 PM   #4
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I'll get a lot of flack about this, but I've mis-matched batteries on campers for years with no ill effect. Just had matching batteries on this 2012 because I insisted the dealer put them in because our trade in had 2 batteries.(unmatched for 4 yrs) with no switch to select on or the other or both either.
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Old 03-26-2015, 06:19 PM   #5
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Quote:
Originally Posted by OldCoot View Post
I'll get a lot of flack about this ...
Better you than me, but that's why I asked.



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Old 03-26-2015, 07:14 PM   #6
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These details may require that I buy 2, anyway:

The DP24 is rated at 65AH at the 20-hour rate. The DC27 is rated at 90.

My wife and I both use CPAP. Combined, they draw 8 amps. That's 64AH overnight.
If I used a switch and ran only the DP24, I'd kill it. If I did the same with the DC27, it would use 72% of capacity.

If I wish to avoid exceeding 50% depth of discharge, the only way to do that would be using them in parallel. In that configuration, would the discharge at the same % rate? Might that mean that the DC27 is discharging into the DP24? Even if so, I'm okay with a little inefficiency if it doesn't result in long-term damage.

If it matters if they charge separately, I could use the switch to isolate them while charging and put them in parallel overnight? Would charging separately require running the generator longer?
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Old 03-26-2015, 07:23 PM   #7
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Just me being me, I would hook them together in parallel without a switch and go on about my business. It might not be the ideal situation, but it's been happening on diesel trucks for years and years before rv's used dual batteries. It might shorten the life on one battery a little but I have seen folks do it all the way back in the 50's and 60's with 6v batteries on tractors, big trucks, etc. I think you are worrying about nothing. JMHO.
I also wouldn't worry about charging them separately either.
Let the flack start!
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Old 03-26-2015, 07:24 PM   #8
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The biggest concern with using different ( age/size) batteries is with charging as they will charge differently and eventually one will fail early. If you have the switch shown, you can use the both position when drawing power from the battery and then select only one to charge them separately. Not the ideal situation, but unless you plan to do this forever it should be OK.
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Old 03-26-2015, 07:56 PM   #9
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For the same money or less you can get a couple Interstate GC2 golf cart batteries at Costco. These are true deep cycle batteries and will give you much more capacity than two marine batteries in parallel. I paid $83 each. Here is my cost breakdown:

$83 (I had one core to give)
$83 ($15 core charge)
$6.99 for series cable from Napa auto parts
$12.50 x2 for GC2 battery boxes
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Old 03-26-2015, 08:11 PM   #10
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I don't have a Costco anywhere near me. Also, if they're 6v, that won't work for me. The batteries will serve a dual purpose in which they'll be used separately, when not camping.

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