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Guest Message by DevFuse

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dual battery question

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5 replies to this topic

#1 archemitis


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Posted 03 January 2004 - 09:29 AM

what if i ran one normal car sized battery, linked up to a smaller motorcycle gel battery. i can get them easy, and cheap. they have about 250 cca on average. if they are both 12 volt, and i hooked them together, wouldnt it be like having a bigger battery? or would the smaller one hinder the bigger one?

#2 torxxx


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Posted 03 January 2004 - 03:44 PM

you'd have to series paralell the wires to make it so it wasnt making 24 volts

and it will only work if both batteries are kept charged.. (you'd have to split the wire off the alternator that goes to the battery and make it so you could hook it to both.

#3 MilesFox


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Posted 03 January 2004 - 09:23 PM

if this is for an 8a81 with an ea82 motor........

you can relocate the battery on the ea81 body to the other side. use ea82 cables. connect the alt to that post.

then on the other side, use athe other battery. yhe stock positive cable will plug into the fuse link panel. use the body cround on the negative terminal. the battery will charge thru that

But 2 batteries will draw more from the alt, i had voltage spikes with mine. so an isolator or bigger alt.

what i liked about mine is the battery on the right was for cranking the motor, and the one on the left supplied the car, charged thru the car. over there would be ideal for a marine deep cell bayyery

#4 subarubrat


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Posted 03 January 2004 - 09:42 PM

Just get a battery isolator, a good one will manage the of the second battery charging completely.

#5 Bugaru


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Posted 03 January 2004 - 09:57 PM

Having two batteries would be nice, depending on how you connect them.

"Series paralell" is a contradiction in terms.

Connecting two 12v batteries in "parallel" (negative to negative and positive to positive) would keep the system at 12 volts but give you a higher current.

Connecting two 12v batteries in "series" (positive terminal of one battery is connected to negative terminal of the other) would give you higher voltage, 24 volts. In a 12v system, this would cause havoc.

Charging the batteries in parallel (with the charge wire from the alternator connected only to the primary battery) would charge both batteries equally, as long as both of the batteries have the same amp hour rating and are of about the same age. Remember, the current will follow the path of least resistance, so if you have both an older and newer battery hooked up, the older one (with more internal resistance) is less likely to get charged, regardless of a single or split connection to the alternator.

Another thing to consider is:
Connecting a diode in between the two positive terminals(restricting the flow to the spare battery to In and not Out) would keep that battery charged but not allow it to be drained. Then you could use a bypass switch to cut out the diode and get that extra current when you want it. That way you should always have a charged battery, unless you forget to flip the switch back.

If it is cca you are concerned about, you could go with a larger battery, in my 83 wagon I run a Diehard truck/suv battery, it fits in the battery tray nicely, and has a rating of 875 cca.

#6 torxxx


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Posted 03 January 2004 - 10:16 PM

ok my bad on the terms....
I did my wiring bit 5 or 6 years ago so you'll have to excuse me..
I had the concept right, just the terms wrong..

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