6v vs 12v batteries

[road glide]

Yesterday, I installed 4 deep cycle 6v GC2 Deep Cycle Extreme Interstate batteries for my house(2 wired in series = 220 amp hrs total 440). Previous O'Reilly Super Start Marine 12 volt (200 amp hrs - total 400) that lasted almost 7 yrs.
I found these from a private party one year old. (Actually I bought all 6 that he had in his 5th wheel - he switched to Lithium) $360 for all 6).
My goal was a little more amp hrs, possibly longer life and they fit in my tray.
Not a fan of lithium due to requires BMS and I feel more volatile if freezing or over-charged..
The only thing so far, checking the 4 in the tray with my voltmeter they are showing 13.1v but inside the coach my Xantrex 1500 INV/CHGR panel wants to charge them at 14.1-14.2 and the battery indicator lights (red-yellow-green) is just on Yellow. The actual readout on inside panel is 11.99-12.00 which is odd. Unless these deep cells take longer to charge up? or the Xantrex is misreading voltage.
The inside panel has always been a few volts lower than testing at battery tray. But not that much.
IMO - 6 volt deep cycle (thicker plates -lowercost) if they fit is the way to go..

[SteveJ.]

Originally Posted by zibberfitchy

Discharging flooded cell batteries below 50% can severely shorten the life and reduce the capacity of the battery by damaging the internal cells.

To use your tire analogy, imagine buying highway tires for your vehicle then routinely taking them off-road and exceeding the tire speed rating. The more you abuse the tire outside its design conditions, the faster it will fail.

Define severely. This chart shows going from about 1250 cycles at 50% to about 750 cycles at 80%. Yes, a significant drop in cycles but each cycle is supplying 60% more power. The total potential amp hour capacity lost is about 15%. How many extra batteries would one want to install and carry around to gain 15% efficiency? There is a lot more damage done by under or over charging, I'm thinking. Especially under charging.

Now, if you're in a situation where a daily big discharge is happening it would be time to strongly consider lithiums for many reasons.

So really, not a big deal and certainly not severe. For most people the batteries will simply age out before they get anywhere near 1000 cycles, assuming the batteries aren't murdered from poor habits.

This glommed from the Trojan site:

[Mark_K5LXP]

Originally Posted by zibberfitchy

Discharging flooded cell batteries below 50% can severely shorten the life and reduce the capacity of the battery by damaging the internal cells.

If that were true, it would be reflected in published battery data. No such "severe shortening" exists except as RV folklore.

Mark B.
Albuquerque, NM

[Winemaker2]

Originally Posted by zibberfitchy

Discharging flooded cell batteries below 50% can severely shorten the life and reduce the capacity of the battery by damaging the internal cells.



To use your tire analogy, imagine buying highway tires for your vehicle then routinely taking them off-road and exceeding the tire speed rating. The more you abuse the tire outside its design conditions, the faster it will fail.

That is only true if you consider # cycles as your key measure.
I consider total AHs delivered and yes you lose about 10% of total batty capacity with deeper discharge but that's a SMALL loss not a SEVERE loss.
If it were true why wouldn't mfg life cycle charts show a change in slope of the curve above 50% DOD?
50% is a good system design guide but that doesn't mean you can't or should never exceed 50%.
Most battys that suffer short lives are a result of other poor treatment... under / over charging, long duration at partial SOC ( even storing at that magical 50% is not a good practice), lack of watering for FLA.

[SJ-Chris]

Originally Posted by Winemaker2

That is only true if you consider # cycles as your key measure.
I consider total AHs delivered and yes you lose about 10% of total batty capacity with deeper discharge but that's a SMALL loss not a SEVERE loss.

50% is a good system design guide but that doesn't mean you can't or should never exceed 50%.
Most battys that suffer short lives are a result of other poor treatment... under / over charging, long duration at partial SOC ( even storing at that magical 50% is not a good practice), lack of watering for FLA.

^^^ This


There is a graph above that shows at 50% DOD you'd get ~1200 cycles and at 80% DOD you'd get about 750 cycles. Let's consider 1 cycle = 1 day. Here's a great question.... What % of RVers do you think ever BOONDOCK 750 nights in their RVs or trailers?? I'm guessing less than 5% of RV owners. The "average" RV user uses their RV 20-30 nights per year, and many of those nights will be with full hookups. If the average RVer boondocks 20 nights per year then 750 cycles would take them 37.5 years to "use up" all their battery cycles. Do you see now why FOR MOST RVers this "don't discharge more than 50%" mantra makes absolutely no sense?


To each their own of course. Really makes no difference to me how many batteries other people have and how low/high they discharge their batteries. Have fun out there and go camping!


-Chris

[Persistent]

Originally Posted by zibberfitchy

Discharging flooded cell batteries below 50% can severely shorten the life and reduce the capacity of the battery by damaging the internal cells.

To use your tire analogy, imagine buying highway tires for your vehicle then routinely taking them off-road and exceeding the tire speed rating. The more you abuse the tire outside its design conditions, the faster it will fail.

This is flat out not true. Most deep draw lead acid batteries can be discharged down to 10% state of charger for approximately 300 times. They are laboratory tested for this at the 20 hour discharge rate.

Each discharge down to 50% state of charge counts as 1/2 discharge cycle. The best battery manufacturers post these technical tests for all to see.

You must fully recharge soon after discharge to get this performance. If you store them discharged sulfation occurs. Sulfation does shorten life and reduce capacity. Storing 3 months at 50% state of charge will probably kill the batteries altogether.

You can repeat these tests in your own garage if you get some basic electrical equipment and real knowledge about electricity and battery chemistry.

"The truth is out there!"

[Winemaker2]

Originally Posted by SteveJ.

Define severely. This chart shows going from about 1250 cycles at 50% to about 750 cycles at 80%. Yes, a significant drop in cycles but each cycle is supplying 60% more power. The total potential amp hour capacity lost is about 15%. How many extra batteries would one want to install and carry around to gain 15% efficiency? There is a lot more damage done by under or over charging, I'm thinking. Especially under charging.



Now, if you're in a situation where a daily big discharge is happening it would be time to strongly consider lithiums for many reasons.



So really, not a big deal and certainly not severe. For most people the batteries will simply age out before they get anywhere near 1000 cycles, assuming the batteries aren't murdered from poor habits.



This glommed from the Trojan site:

Steve while I agree with your conclusions, I get very different #s when I do the math

Assume a 100 AH batty

1) discharge to 50% DOD 1250 cycles
100 AH X 0.5 X 1250 = 62,500 AH delivered for batty life

2) discharge to 80% DOD 750 cycles
100 AH X 0.8 X 750 = 60,000 AH delivered for batty life

2500 AH loss ÷ 62,500 AH = 0.04 = 4% loss of delivered AH

This is hardly a SEVERE loss!

When I looked at several cases & batty types I saw < 10% loss in most cases.

Yet the 50% MYTH continues to be repeated by those that don't understand that # cycles is not a meaningful measure.
In fact the loss is much more severe when a user goes from 10% DOD to say 20% DOD or 30% DOD... does that PROVE you should install batty banks 10X what is required???

[theoldwizard]

Originally Posted by road glide

I found these from a private party one year old. (Actually I bought all 6 that he had in his 5th wheel - he switched to Lithium) $360 for all 6).

Great price if they were not abused and you have the space to install them and the weight is within your capacity !

[theoldwizard]

Originally Posted by Winemaker2

Steve while I agree with your conclusions, ...

I am not going to get into this DOD-Life Expectancy discussion (NOT a Chemist or an expert in batteries) but I will say, the most COMMONLY AVAILABLE lead-acid batteries SPECIFICALLY DESIGNED for deep discharge are golf cart batteries (GC2).

Any battery that has a "Cold Cranking Amp" (CCA) or "Marine Cranking Amp" (MCA) rating is NOT primarily intended for deep discharge !

If this is what you can afford, go for it ! Just make sure to keep the fluid level up and all connections, case and tray CLEAN ! At least once a year, everything should be disassembled, cleaned and painted if necessary. Watering and thorough cleaning not required on LiFePO4 batteries.

[Winemaker2]

Originally Posted by theoldwizard

I am not going to get into this DOD-Life Expectancy discussion (NOT a Chemist or an expert in batteries) but I will say, the most COMMONLY AVAILABLE lead-acid batteries SPECIFICALLY DESIGNED for deep discharge are golf cart batteries (GC2).

Any battery that has a "Cold Cranking Amp" (CCA) or "Marine Cranking Amp" (MCA) rating is NOT primarily intended for deep discharge !

If this is what you can afford, go for it ! Just make sure to keep the fluid level up and all connections, case and tray CLEAN ! At least once a year, everything should be disassembled, cleaned and painted if necessary. Watering and thorough cleaning not required on LiFePO4 batteries.

So why quote a discussion re DOD and cycle life?