# Real Life Lead Acid



## major (Apr 4, 2008)

A friend has a Gem NEV. He had his battery set go south and I helped him test those and choose a new set. He got six 12V deep cycle flooded group 31 size batteries rated 130 Ah 20 hour rate. I charged each battery with a very good 12V, 25A charger. Then I tested each on the test stand with equal conditions. Here is the chart:










As you can see, the time it takes to fall to 10.5 V varies quite a bit giving a range in charge and energy of close to 20%.

If one were to use the nominal specs like this: 12V * 130Ah * 6 batteries = 9.36 kWh. A pretty decent sounding figure for the size and cost.

However, just adding the tested kWh figures, it shows only 3.67 kWh. 

And, it would likely be less because you would not be able to fully discharge the strong batteries without taking the weaker ones completely flat. Like they say, your team is only as fast as the slowest horse.

I just thought I would post this for the benefit of those considering Pb-Acid.


----------



## ruckus (Apr 15, 2009)

Sure, those numbers are terrible, but if he ran a dc-dc to power his charger from the battery he could charge as he drives and keep everything nice and full... <:|

What's funny is over here nobody would consider lead, but over at the evdl you have tons of folks convinced that lead is awesome and lithium is sketch.

go figure...


----------



## Ziggythewiz (May 16, 2010)

Cool data. I assume your cutoff was 10.5V under sag? I'd expect that to be around 65% DOD.

That's what sucks about lead, you can only count on 30% sticker for daily use.

For anyone stuck on lead (mentally) I think a day of balancing lithiums would do wonders. It would be surprising how much juice they can hold if you hadn't calculated it already.


----------



## tomofreno (Mar 3, 2009)

Nice data major, thanks! Good to see data on the variability. I've posted the curve below several times here, but thought it might be good to compare. It gives corrected Ah capacity for several lead acid batteries taking account of Peukert using equations from the Smart Gauge Electronics site. The Odessy 2250 batteries have a 126 Ah capacity at the 20 hr rate, similar to your 130Ah. The curve shows about 80 Ah capacity at 90 A discharge current. The T-1275's are 150Ah at the 20 hr rate and show about 93 Ah at 90A discharge current. So if anything, maybe the curves are optimistic.
View attachment Peukert graph.pdf


----------



## major (Apr 4, 2008)

Ziggythewiz said:


> Cool data. I assume your cutoff was 10.5V under sag? I'd expect that to be around 65% DOD.


1.75V/c is the standard cutoff point for load tests on Pb-Acid. After that, ain't much left  Certainly not another 35%. I didn't want to stress these due to the fact that they aren't mine.


----------



## Ziggythewiz (May 16, 2010)

I've done another 6 miles after sagging to 9v. The first time wasn't intentional


----------



## major (Apr 4, 2008)

Ziggythewiz said:


> I've done another 6 miles after sagging to 9v. The first time wasn't intentional


If I had continued the test at that same load, it would have tanked before another couple of Amp hours. I know because I've done it many times. Now when you're running a very high load, the sag (IR drop) will take you below 1.75V/c before you get to the knee. But I ran these curves at less than 1C.

Here is Batt #1 from the same test as in post #1. I just let it sit for two hours, open circuit. Then I put it back on the test stand under the exact same conditions as before (same resistance load).


----------



## major (Apr 4, 2008)

tomofreno said:


> Nice data major, thanks! Good to see data on the variability. I've posted the curve below several times here, but thought it might be good to compare. It gives corrected Ah capacity for several lead acid batteries taking account of Peukert using equations from the Smart Gauge Electronics site. The Odessy 2250 batteries have a 126 Ah capacity at the 20 hr rate, similar to your 130Ah. The curve shows about 80 Ah capacity at 90 A discharge current. The T-1275's are 150Ah at the 20 hr rate and show about 93 Ah at 90A discharge current. So if anything, maybe the curves are optimistic.


I almost feel like doing a C/20 discharge just to check. But that is a long day at the office  The spec also listed 105Ah at C/5. And I think I can fashion a constant current rig for that level (26A). Maybe I'll try that.

BTW, these new batteries are like about 3 times better than 5 of the 6 old ones he has. And the sixth one had a bum cell which went to zero after about 10 Ah. Actually I think he'll be very happy with these new ones.


----------



## GerhardRP (Nov 17, 2009)

major said:


> 1.75V/c is the standard cutoff point for load tests on Pb-Acid. After that, ain't much left  Certainly not another 35%. I didn't want to stress these due to the fact that they aren't mine.


If you havn't recharged them yet, could you measure the resting voltage to estimate the actual SOC. I note that the weakest battery shows the greatest rebound, so it might be resistance rather than capacity that is off.
Gerhard


----------



## piotrsko (Dec 9, 2007)

FWIW: have you tested and correlated the specific gravity? I found mine to vary, but didn't do anything other than adjust.


----------



## tomofreno (Mar 3, 2009)

major said:


> ...BTW, these new batteries are like about 3 times better than 5 of the 6 old ones he has. And the sixth one had a bum cell which went to zero after about 2 Ah. Actually I think he'll be very happy with these new ones.


 Yeah, all depends on the need. Not everyone needs 75 mile range or 1000A. Great to see real data.


----------



## major (Apr 4, 2008)

GerhardRP said:


> If you havn't recharged them yet, could you measure the resting voltage to estimate the actual SOC. I note that the weakest battery shows the greatest rebound, so it might be resistance rather than capacity that is off.
> Gerhard


Too late  Already recharged. The internal resistance looked to be consistent at the beginning of the test. But interesting observation about the larger rebound on the weakest horse.



piotrsko said:


> FWIW: have you tested and correlated the specific gravity? I found mine to vary, but didn't do anything other than adjust.


No, it's been years since I tested floodies and I didn't even think about SG.

Anyway, Dave wants his Gem back so he can use it before the snow flies. I can't turn this into a science project. We'll just have to live with the data I was able to get. I've seen similar capacity variation on other batches of Pb-Acid so this doesn't totally surprise me. I was just pleased I didn't find any real bad ones. That is really what I was looking for


----------



## Ace_bridger (Nov 22, 2011)

Great data and it really highlights the limitations of lead acid.

Despite the inadequacies of lead I put 12 T-1275 Trojans in my Golf but then the car is generally used to do my 10 mile round trip commute and it's all in 30mph limit.

Lead meets my spec but if I used the car as a normal daily driver and I needed decent range and speed then lithium it would be. A quick calc tells you that the lithium cost per mile, over the life of the batteries, is a fraction of the cost of lead...but in my case lithium would have been awesome but way over spec'd.

Thanks for publishing your data, very useful and enlightening.


----------



## quickcharge (Aug 15, 2009)

I realize the short comings of lead acids, but, your discharging those batteries at a very high rate, no wonder you don't get many minutes, and get so little AH out. Not really a fair evaluation of what they could do if discharged at a rate they were designed for.


----------



## Ziggythewiz (May 16, 2010)

We don't ask what the battery was designed to do, we ask what the battery can do for us. Major's test was nearly a typical load one would ask from the batteries while driving, which is relevant to us.

My first pack was designed for a C/125 rate, so it should be able to power a night light for a week. Who cares? Why would anyone test that?


----------



## major (Apr 4, 2008)

quickcharge said:


> I realize the short comings of lead acids, but, your discharging those batteries at a very high rate, no wonder you don't get many minutes, and get so little AH out. Not really a fair evaluation of what they could do if discharged at a rate they were designed for.


Hi quick,

I don't think 95 Amps is particularly high for a 130 Ah battery. It is less than 1C. I do realize that in the Gem, the typical average battery current may be below my test current. But I also disagree that my discharge rate is higher than what the battery was designed for. And my test was simply "a test" and neither fair nor unfair. The product is what it is and my test simply showed how it preformed at a selected load which coincided with the resistor value on my test stand. 

I mentioned that I was primarily looking for a "bad" battery or cell so I could feel reasonably confident about installing them in Dave's Gem. I posted the results for the benefit of the membership. I'm glad you took notice.

Regards,

major


----------



## major (Apr 4, 2008)

major said:


> BTW, these new batteries are like about 3 times better than 5 of the 6 old ones he has. And the sixth one had a bum cell which went to zero after about 10 Ah. Actually I think he'll be very happy with these new ones.


Here is a chart of the old batteries: 









I ran this test with the 6 batteries in the vehicle and connected the series string to my regulated load bank and monitored voltage with six DVMs and a stop watch. The regulator kept faulting out at 75 Amps, so I turned it down to 50A at about 8 minutes. I took the readings into Excel and integrated for Ah. Not too precise of a test, but showed the trends.


----------



## major (Apr 4, 2008)

major said:


> I've seen similar capacity variation on other batches of Pb-Acid so this doesn't totally surprise me.


I ran across this, so WTH.


----------

