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Old 01-23-2020, 10:20 PM   #1
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Another battery question

We have a Cherokee 274VFK and the battery is located in a compartment in front. I would like to install two AGM batteries. Sam's has 12 volt group 31 AGM.
When I look at 6 volt GC2 AGM the CCA is listed. I was in a Batteries + bulbs store today and the lady helping me said all AGM batteries are dual purpose.

It looks like AGM GC2 6 volt batteries are not really deep cycle.

Should I go with two 6 volt or the two 12 volt? I would go with the GC2 AGM if it was a true deep cycle. The GC2 AGM is quite a bit more expensive thatn the Group 31 12 volt AGM.

Thanks for any suggestions,

Willie
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Old 01-24-2020, 02:43 AM   #2
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AGM batteries can be discharged down to 20% compared to 50% for flooded deep cycle. So I would say the battery lady doesn't really know what she is talking about.

At the 20 hr discharge rate a pair of Group 31 = 210 AH and a pair of GC2 = 190 AH. So I would go with the Group 31.
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Old 01-25-2020, 11:24 PM   #3
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Boondocking,
Thanks for the reply. I will go with the two 12 volt group 31. I'm not sure how much boondocking we will do. I'm trying to get set up so we can give it a try.
Thanks again,
Willie
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Old 01-26-2020, 12:23 AM   #4
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Cycling your battery bank down to 20% capacity, even with agm batteries, will significantly shorten your battery life and increase your kwh life cycle cost.

This is a good site to look at for factual battery information.
https://www.solar-electric.com/learn...tery-faq.html/
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Old 01-26-2020, 12:47 AM   #5
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Quote:
Originally Posted by SlowrideHD View Post
Cycling your battery bank down to 20% capacity, even with agm batteries, will significantly shorten your battery life and increase your kwh life cycle cost.

This is a good site to look at for factual battery information.
https://www.solar-electric.com/learn...tery-faq.html/
Totally agree. There really isn't much difference in the cycle life of AGM and FLA with a 50% discharge. That being said the Peukert's constant of an AGM battery is much lower than a FLA so if you have high current draws, the same amount of current draw on an FLA, will cause your SOC to go much lower on the FLA vs an AGM.
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Old 01-26-2020, 01:30 AM   #6
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Quote:
Originally Posted by SlowrideHD View Post
Cycling your battery bank down to 20% capacity, even with agm batteries, will significantly shorten your battery life and increase your kwh life cycle cost.

This is a good site to look at for factual battery information.
https://www.solar-electric.com/learn...tery-faq.html/
Quote:
Originally Posted by babock View Post
Totally agree. There really isn't much difference in the cycle life of AGM and FLA with a 50% discharge. That being said the Peukert's constant of an AGM battery is much lower than a FLA so if you have high current draws, the same amount of current draw on an FLA, will cause your SOC to go much lower on the FLA vs an AGM.
If you want some real factual information about the 80% AGM discharge instead of hearsay, go to the site below.
https://batteryuniversity.com/learn/..._glass_mat_agm
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Old 01-26-2020, 11:10 AM   #7
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Originally Posted by boondocking View Post
If you want some real factual information about the 80% AGM discharge instead of hearsay, go to the site below.
https://batteryuniversity.com/learn/..._glass_mat_agm
Or if you want some REAL information just go on the Trojan site. They have the discharge vs cycles charts on THEIR AGM and FLA batteries, instead of the hearsay on the Battery university site. You will see they are close for 50% discharge and 80% discharge. You lose a lot of cycles going from 50% to 80% for either battery.


Don't get me wrong, I prefer AGM over FLA for a number of reasons. Just don't believe that you should regularly discharge AGM to 80%.
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