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Old 09-05-2018, 11:52 AM   #1
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Yes, another battery question.

Always told it is not wise to mix new batteries with old batteries. Can someone tell me why?
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Old 09-05-2018, 01:00 PM   #2
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I assume you're talking about batteries within a single bank of batteries. The batteries in a bank will equalize across the set of batteries and the weakest one will drag the others voltage down to its level.
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Old 09-05-2018, 01:35 PM   #3
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I assume you're talking about batteries within a single bank of batteries. The batteries in a bank will equalize across the set of batteries and the weakest one will drag the others voltage down to its level.
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Old 09-05-2018, 02:54 PM   #4
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It depends on how you connect them and I am referring to lead acid stuff. If connected in series....such as 2 golf cart 6V lead acid in series, then mixing an old battery with a new one is not a good approach. Battery charge acceptance has a lot to do with age along with the number of charge cycles plus the depth of discharge.

In series, both the charge and discharge currents pass through each in series battery. So an old battery can restrict the charge acceptance in the new one.

Now with parallel connections, each battery will see what ever voltage is applied by the charger and charge accordly. Now there is controversy where claims that an old battery will pull charge from a newer one. Generally this is nonsense! Now sure, if the old battery short circuits then the entire bank is at risk.

In parallel each will charge according to its own charge acceptance. On discharge, each will supply charge until they cannot. Do some research, avoid getting sucked in with ''don't ever do that recommendations.''

Electrical Myths, Part 3: Mixing Batteries of Different Ages/Capacities - RV Nerds

/www.amplepower.com/pwrnews/parallel/index.html
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Old 09-07-2018, 01:52 PM   #5
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With parallel batts only 12V batts can be used not 6v deep cycle.

There are 12V deep cycle but they usually do not have the same punch 2 in parallel compared to 2 golf carts in series.
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Old 09-07-2018, 06:03 PM   #6
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With parallel batts only 12V batts can be used not 6v deep cycle.

There are 12V deep cycle but they usually do not have the same punch 2 in parallel compared to 2 golf carts in series.

Not really, for example I have two battery banks consisting of 4 golf carts in series/parallel for each bank.

I configured these banks using new batteries from Sams which seems to continuously be closing stores
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Old 09-08-2018, 05:53 AM   #7
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"I have two battery banks consisting of 4 golf carts in series/parallel for each bank."


The 6v in series should be the same age.
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Old 09-08-2018, 07:54 AM   #8
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"I have two battery banks consisting of 4 golf carts in series/parallel for each bank."


The 6v in series should be the same age.

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Old 09-10-2018, 10:09 PM   #9
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Ok, reading this, I want to make sure I get it.

I have a house bank of 2 6 volt batteries hooked up to make a 12 volt unit. Those batteries got run down a little but are only a year old, so they still have some life.

I understand from the above that I can add in parallel another 2 new 6 volt batteries if I hook the 2 new batteries together to make a 12 volt unit. Have I got that right?
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Old 09-11-2018, 08:35 AM   #10
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Ok, reading this, I want to make sure I get it.

I have a house bank of 2 6 volt batteries hooked up to make a 12 volt unit. Those batteries got run down a little but are only a year old, so they still have some life.

I understand from the above that I can add in parallel another 2 new 6 volt batteries if I hook the 2 new batteries together to make a 12 volt unit. Have I got that right?

That is the way I would do it.
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Old 09-14-2018, 08:46 AM   #11
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With parallel batts only 12V batts can be used not 6v deep cycle.

There are 12V deep cycle but they usually do not have the same punch 2 in parallel compared to 2 golf carts in series.
Typically, two 12V batteries in parallel will have less internal resistance than two 6V in series and about the same AH capacity. So more 'punch' for things like inverters etc.
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