amp hours (ah) for 6v vs. 12v

[macnut]

Many people look at ah ratings to compare batteries. I was at a dealer today and said I was thinking of replacing my house batteries (2) with 100ah Lifetime AGM 12V batteries because we use the motorhome about once a month for three nights (otherwise, it's in inside storage without power) and we usually dry camp in a state park. He recommended Interstate 6v RV lead-acid batteries because each one was rated 232ah, so two would give me twice the power of the AGM batteries.

However, after thinking about this, the 6v batteries are 232ah at 6v, but half that (or 116ah) at 12v. So they only provide about 16% more power.

Can someone confirm this is the correct way to calculate 6v vs. 12v battery amp hours?

He also said you could use more of the available power in the 6v battery. The 12v AGM recommends drawing down only 50% of the power, but you could take the 6v lead-acid battery well below that without harm. Can anyone also confirm that is true?

Thanks!
Al

[autofish]

Macnut....first no battery should br drawn down below 50% if you want them to last. Now asfar as amp hr of 12 volt vs 6volt 2@ 12v at 100amphr each = 200 amp hr 12v and 2each 6v at 232amphr each will be 12volts at 232 amphr, so the 6v batteries win by 32 amphr. but in gereral 6volt batteries hold up much better and most use 4 of the 6volt if they have the space.

[macnut]

Autofish, much appreciated!

Al

[Barlow46]

Macnut,
Here is some good reading for you. I frequently use it as a reference when I start trying to "outthink" my system.
The 12volt Side of Life (Part 1)

[macnut]

Originally Posted by Barlow46

Macnut,
Here is some good reading for you. I frequently use it as a reference when I start trying to "outthink" my system.
The 12volt Side of Life (Part 1)

Barlow46, this is the best information I have see so far. I will read and also keep it on my iPad so i have it handy when needed...
Thanks!!
Al

[TXiceman]

Originally Posted by macnut

Many people look at ah ratings to compare batteries. I was at a dealer today and said I was thinking of replacing my house batteries (2) with 100ah Lifetime AGM 12V batteries because we use the motorhome about once a month for three nights (otherwise, it's in inside storage without power) and we usually dry camp in a state park. He recommended Interstate 6v RV lead-acid batteries because each one was rated 232ah, so two would give me twice the power of the AGM batteries.

However, after thinking about this, the 6v batteries are 232ah at 6v, but half that (or 116ah) at 12v. So they only provide about 16% more power.

Can someone confirm this is the correct way to calculate 6v vs. 12v battery amp hours?

He also said you could use more of the available power in the 6v battery. The 12v AGM recommends drawing down only 50% of the power, but you could take the 6v lead-acid battery well below that without harm. Can anyone also confirm that is true?

Thanks!
Al

Two 6 volt, 232 amp-he batteries in series will provide 12 volts an 232 amp hours.

If you have two 12 volt, 150 amp hour batteries in parallel, you will have 12volts and 300 amp hours.

In either case you do not want discharge the batteries below 12.06 volts.
http://www.dcbattery.com/faq.html


Ken

[Barlow46]

Ken,
When reading "12v side of life", I came across this statement.

"a pair of group 24 12 volt batteries only provide 140-170 amp/hours of capacity, where a pair of golf cart batteries provide 180-220 amp/hours."
The 12volt Side of Life (Part 1)

Your post is saying two 12v 150a batteries in parallel will double the amp hrs. to 300. This is also what I understood in the past. What would be the reason for the discrepancy?

[paz]

Originally Posted by Barlow46

Ken,
When reading "12v side of life", I came across this statement.

"a pair of group 24 12 volt batteries only provide 140-170 amp/hours of capacity, where a pair of golf cart batteries provide 180-220 amp/hours."
The 12volt Side of Life (Part 1)

Your post is saying two 12v 150a batteries in parallel will double the amp hrs. to 300. This is also what I understood in the past. What would be the reason for the discrepancy?

Group 24 is a small battery. That is the reason for the lower amp-hour rating, not the voltage.

To evaluate the capacity of 6V vs. 12V batteries remember that for a pair of 6V batteries wired in series, the voltage doubles but the amp-hour rating remains the same. For a pair of 12V batteries wired in parallel, the voltage remains the same but the amp-hour rating doubles.

As has already been stated, discharging a battery below 50% (12.25V) can shorten its life. That means the effective available amp-hours is only half what the battery or bank of batteries is rated for.

If you decide on 12V batteries, make sure they are true deep cycle. Starting batteries are designed to provide a surge of current over a brief period of time. Deep cycle batteries are designed to provide sustained current over a long period of time and have thicker plates. Therefore, deep cycle batteries can better withstand discharging and recharging than non-deep cycle batteries. Marine batteries are combination batteries (for example, they can be used to start your outboard engine or to power your electric trolling motor), but they are not true deep cycle batteries. Any battery with a CCA (cold cranking amp) rating is a starting battery and is not designed for repeated discharging and recharging.

[macnut]

I appreciate everyone's comments. Because the 6v option will only increase amp hours by 16% (232/200), I am leaning towards the AGM 12v batteries. On the downside they are more expensive and may not last as long. On the upside, they are maintenance free, have a low discharge rate, and can be recharged faster. After hearing responses, I may also need to invest in a better charger, since I now just rely on the converter.

[wa8yxm]

You are seriously conufsed (As may be the sales droid) on battery.

The most common 6V RV battery is a GC-2 Class Golf Car battery, 230 amp hours at 12 volts when properly connected in pairs.

Your two 100 amp hour AGM's (I assume you are NOT buying them at Wal-mart) will give you 200 amp hours.

in both cases you can safely use 1/2 fo that capacity.

One of the reasons I do not like threads with "12/V V/s 6V amp hours" Is that I have not exactly held in my hand, but towed on my (rented U=Haul) Trailer a single 12 volt battery that was in the thousand amp hour range,, If not larger. And it was a true deep cycle as well.

The battery rebuilder who lent it to the club I represented loaded it on the trailer with a fork lift,, The fork lift was powered by in identical battery.

Oh, it was flooded wet cell too.


But back to the facts.

Your six volt pari is 230 amp hours

your 12 volt AGM pair, is 200 amp hours

Yes that's very close, enough (15%) to be "Significant" in a 10 percent world, but not enough to worry me.

The question is this.

Is the higher cost of AGM worth the low maintanence?

[macnut]

I believe our last posts said basically the same thing. I'll weigh the trade-offs and report back in a few months on what I decide.I am thinking of making the change in April. Thanks for all who posted!

[terry735001]

i think some one should talk about AGM s are not good in the cold i lost 2500$ of them over a bad winter and the ones i had where 230lbs 12vs not installed in my RV rv came latter

too i well not use the 6vs over wight and keeping them equalize so the Sade part is
8+4 make 12v and alot of the times thats what happens negative side battery shows 8v positive battery well show 4vs .... so every 3 to 4 months you need to equalize them or one gos bad then to find that one well i am sure you under stand

for some one not going out to much i would go with the higher amp hr 12v

thats just how i feel i am sure there are alot out there that well say 6v are better

[macnut]

Good point about having to equalize the 6v pairs occasionally....even more maintenance.

[Mr_D]

Originally Posted by macnut

Good point about having to equalize the 6v pairs occasionally....even more maintenance.

Uhhh... My Interstate U-2200's lasted just under 10 years and I NEVER equalized them in that time. In fact they were still OK but we were heading out on a trip and I didn't want trouble while on the road.