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Old December 31st, 2005, 06:42 PM   #1
amc78cj7
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Default dual batteries

Optima recommends only hooking dual batteries in parallel when they are of the same make and age.

Why is this?

What will happen if I connect a 3-year old deep cycle yellow top (that still holds full charge) to a brand new red top?

Here is what I have:

Red-top Optima, model 34/78
CCA=800
CCA @ 32F = 1000
Reserve Capacity=110
Capacity (C/20 rate)=50
Internal Resistance = 0.003 ohms
Amp hour not listed on battery top.

Yellow-top Optima, model D34/78
CCA=750
CCA @ 32F = 870
Reserve Capacity=120
Capacity (C/20 rate)=55
Internal Resistance=0.0028 ohms
Amp hour (from top of battery)=65

Last edited by amc78cj7; December 31st, 2005 at 09:43 PM.
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Old December 31st, 2005, 08:07 PM   #2
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DON"T DO IT!

the batteries are just different enough to draw at differnet rates. the batteries are all 12 volt but the Optima's are Gel cell and they only except a low amperage charge as compaired to a lead acid without gel the other thing I have learned about regular batteries is they are easy to cook dry. I was using a 10 amp charger and blew one to smetherines in my barn. it was an old Delco 78-a72 and it was missing the whole top when I found it the next day. luck it didn't burn the whole barn down.
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Old December 31st, 2005, 08:21 PM   #3
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But both mine are gel-cell Optima batteries........ How does your info apply to my setup?
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Old December 31st, 2005, 08:32 PM   #4
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if they are both gel cells they should have the same amp hour rating and cold crank amps. if they're the same then no harm no foul, it should perform fine. what you don't want is one battery creating a draw while the other is over charged.
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Old December 31st, 2005, 09:24 PM   #5
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well, they are both optima gel cells; but all optimas are not created equal. They have different CCA and different amp hour ratings since one is a deep cycle. In fact, they make 2 different yellow tops with different CCA and amp hours.

If I don't run them in parallel (ie, I keep the red top for the starter and the yellow top for the winch), what would be the best way to make sure both are connected to the alternator? If they are not in parallel it would seem that the one not hooked to the alternator would be going dead fast?

Here is what I have:

Red-top, model 34/78
CCA=800
CCA @ 32F = 1000
Reserve Capacity=110
Capacity (C/20 rate)=50
Internal Resistance = 0.003 ohms
Amp hour not listed on battery top.

Yellow-top model D34/78
CCA=750
CCA @ 32F = 870
Reserve Capacity=120
Capacity (C/20 rate)=55
Internal Resistance=0.0028 ohms
Amp hour (from top of battery)=65

Last edited by amc78cj7; December 31st, 2005 at 09:42 PM.
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Old January 1st, 2006, 06:07 PM   #6
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Here is the problem. The charging and discharging properties of the battery are dictated by the chemical makeup of the gel/paste within the battery. Over time this rate can change quite tically depending on the conditions placed upon the battery and usage. Enough so, that if you go to use them in parralell you can quite possibly have one battery draining the other or drain one battery beyond its limits. If you wish to hookup 2 different batteries, I would not advise it without a battery management system like Painless' one.
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Old January 1st, 2006, 06:32 PM   #7
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If I don't connect them in parallel, what is the best way to make sure both batteries are being recharged by the alternator?

Thanks Lothos. I got a similar response on POR.
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Old January 1st, 2006, 07:26 PM   #8
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Quote:
Originally Posted by amc78cj7
If I don't connect them in parallel, what is the best way to make sure both batteries are being recharged by the alternator?

Thanks Lothos. I got a similar response on POR.

Your only options are either in paralell or via a management system. Hook em up in series and you end up with 24volts and that aint pretty. You could wire them to a switch and manually switch between them every so often to keep them charged and leave one on standby. Boat stores will have a switch.
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Old January 3rd, 2006, 12:47 PM   #9
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Jeff get a boat switch or an Isoaltor, as mentioned you have 2 different batteries. So i would not run them in parrelel personally.
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Old January 3rd, 2006, 04:42 PM   #10
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Thanks guys. I had a thread on POR also and have decided to go with the marine isolator / cab control kit from Painless. Part # 40103

http://www.jegs.com/webapp/wcs/store...tegoryId=14517
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Old January 3rd, 2006, 05:31 PM   #11
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my dual yellow tops are dead
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Old January 3rd, 2006, 08:03 PM   #12
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one tip for gell cell battires is to charge them with a 250mil amp charger, they will came back to life and hold the charge longer. look at "battery tender" or one of the other rv style chargers.
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