2 x 6V in Series: Capacity reduced or Not?

[dr_nelson]

Hey y'all,

You guys know I don't know anything about electrical. So, here is a question that started bothering me today...

Let's pretend I have two 6V Golf Cart batteries (Duracell SLIGC125) that are each labelled with a 20Hr capacity of 235 AH. Also, let's pretend I wire them in series.
Google tells me that I would double the Voltage while maintaining the capacity. That would result in a 12V battery bank with a 235 AH capacity. That is actually what I want.

Now, my question: Is the capacity of that battery bank still 235 AH (20Hr capacity)? Or is it only half of it, like 117-ish AH?

 

[Zizzer_Zazzer_Zuz]

In rough math yes 117 usable Ah. Keep in mind that usage os like a ball rolling down a hill it will be moving faster as it gets closet to the bottom. The nearer you get to 50% the faster those Ah get used.
Hopfully one of the smarter folks will come along and improve on my gross oversimplification.

Sent from my SM-G920V using Tapatalk

 

[Wabbit]

Dr_Nelson, you are correct.

 

[John61CT]

The actual capacity when new is 235.

The Usable capacity is around half that, since going much below 50% more than rarely will reduce their lifespan.

There are much more expensive bank chemistries that are​ OK drawing down further, and have more lifetime cycles, but big upfront investment.

 

[Optimistic Paranoid]

1:  Your math is correct.  That battery bank would be rated as 235 amp hours.

2:  Remember that with ANY Lead-Acid chemistry battery, whether flooded, AGM, or Gel; 6 volt cases or 12 volt cases, the ACTUAL, USABLE amount of power you can SAFELY use is always 50% of the battery bank's amp hours.  That's just the nature of the chemistry we're dealing with.

 

[galladanb]

Hi DR... Great question!

And some great answers!

I wondered the same thing! Now I know!
Confirmation is a really good thing to have... RIGHT?

Such Fun!

 

[dr_nelson]

Thank you all! Very glad to hear that I do not have to get four 6V batteries.

 

[DLTooley]

I like 20% as a working goal. I don't have to worry about save if there is cloudy weather, and if same is more than a couple of days that is a good reason to spend a day in town and top things off with the drive.

 

[John61CT]

If you mean you prefer to not discharge more than 20% (IOW 80% SoC), it's true your bank will live LOTS longer, but you're doubling your space, weight and initial outlay.

If you're drawing down TO 20% SoC (80% DoD) you're quick-murdering your bank.

Except for LFP, or in lead Firefly Oasis and maybe some Odyssey AGM.