How to charge both batteries on a 2 battery parallel hookup

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djw2112

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With 2 batteries Bat A being the main battery and Bat B being the additional battery.  To hook them up parallel you put neg to neg and pos to pos.  This will make your power last longer.

However my question is how to property charge both with the RV.

If hooked the RV leads up to Bat B it will only charge Bat B, so does that mean that if hooked up to Bat A that:

1. It will only charge Bat A
2. It will charge both batteries.

?
 

Back2PA

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If two batteries are hooked up in parallel (pos to pos, neg to neg) attaching the charger to either will charge both
 

djw2112

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Thanks, I thought so too but then I saw a video that said that hooking it up to the Bat B will only charge Bat B.  Lets say 3 other confirmations here will be how it is.  Can two more people confirm that "either or" will charge both?
 

Back2PA

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djw2112 said:
I saw a video that said that hooking it up to the Bat B will only charge Bat B. 


There are also videos that say the earth is flat, vaccines are a conspiracy, and that chemtrails are being used for population control. Some of these have tens of thousands of views. I would suggest researching to obtain knowledge and understand the system in question, rather than seeing which side gets more votes. But that's just me.
 

John From Detroit

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Two batteries hooked in parallel charge as one
Now if they are different sizes. say a group 24 and a group 31.. Total capacity about 200 amp hours. THen the Group 24 (about 70 amp hours) will take 35 percent of the charge current and the group 31 will take the remaining 65 percent (note that is the ratio of the capacities) so they both reach full charge.. at exactly the same instant.. Likewise when providing power the 35/65 ratio will hold.  There are many myths.. If they are identical in size then tis 50/50 all the way

Two batteries in SERIES must be the same .. size. age. capacity. make, model and so on. THE SAME twins to the highest degree possible.. Else bad things can happen.  But this only applies in series.

Two Six volt GC-2 in series become two halves of a single 12 volt battery for all intentd and purposes including charging.

this covers both "2 battery" setups.
 

grashley

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If you have wires running from battery A to battery B as described, and these are connected on the battery terminals, then the charge simply goes where it is needed most.  The wires make them one power source.

Folks who say otherwise do not understand electricity.
 

xrated

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OK, having been a Journeyman Maint. Electrician since 1980, I will assure you that unless there are some issues with one of the batteries or a wiring issue (loose or corroded connection point), they will both charge. 
 

Gary RV_Wizard

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There are some conditions where multiple batteries hooked in parallel may not charge quite equally if the charge source is applied at one end of the string. It may be a consideration in large banks of very big batteries, but almost surely insignificant with a couple of modest sized 12v's. Sometimes the difference between the optimal method demonstrated in the lab and the everyday practical one in the field just ain't worth worrying about.
 

thesameguy

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Gary RV_Wizard said:
There are some conditions where multiple batteries hooked in parallel may not charge quite equally if the charge source is applied at one end of the string. It may be a consideration in large banks of very big batteries, but almost surely insignificant with a couple of modest sized 12v's. Sometimes the difference between the optimal method demonstrated in the lab and the everyday practical one in the field just ain't worth worrying about.

Yes, this. Also there could be some variables with modern smart chargers if the batteries are of a different size or type or even brand or age - and that could potentially be dangerous. But these are ultimately subtle variables in the final result. If the batteries are connected together they charge together - for better or worse! I maintain the batteries in my dual battery Suburban and Cadillac with the same simple 12v battery charger.

For grins, I would love to read more from the guy who claims they wouldn't! I'd like to see his reasoning.
 

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