12v Lead Acid Batteries for Battery Backups - Discussion

Thread Starter

Lumenosity

Joined Mar 1, 2017
470
A few things I've learned about them.....please feel free to correct or add to this. Not an expert...just a frequent flyer.
Mu observations and conclusions......(ymmv)

1). Failure is often related to them drying out over time. Even though they're sealed...they vent.

2). Deep discharge (such as when the power goes out and stays out for a long time and runs the batteries down) damages the batteries

3). Periodic desulfation can extend the useful life of an SLA battery

4). Checking the water level and topping it up with DISTILLED water can greatly extend their useful life

5), Brand NEW SLA batteries often come a bit on the dry side and could use some distilled water


Point 1
Opening them (yes they can be opened) and adding distilled water once or twice a year to keep them from drying out.

Point 2
These usually aren't "deep cycle" batteries per se. Just regular lead acid batteries.

Point 3
All lead acid batteries work by sulfation and desulfation. Sometimes the don't completely desulfate through regular use

Point 4
Again, the still vent even though they are sealed and lose moisture over time. A dry battery is not a happy battery.

Point 5
I've opened brand new SLA batteries and most of the time they are what I would consider a bit on the dry side. Not AGM batteries. Just SLA.


So, let's say you have an APC XS 1300 Back-Ups unit and it is connected to your PC and a couple other items with a load of 150watts.
As long as that battery is never discharged, it "should/could" last about 3-5 years. But the moment you have a power failure and the battery discharges, lead sulfate forms on the plates. Ideally, when the power comes back on, that process is reversed and the lead sulfate is converted back into lead and deposited on the plates. That's the Perfect World. In reality, the process is never totally efficient and a bit of lead sulfate remains. Over time this sulfate hardens and becomes permanent. Removing hardened lead sulfate crystals is hard. That's why periodic desulfation works best before a lot of time has passed or before the crystals harden. I use solar panels for desulfation. They work better than the "Professional Battery Desulfator" I paid good money for.
 

N11778

Joined Dec 4, 2015
174
Good Idea on the solar panel.
What size panel R U using _____ma.
I also agree that you would have to add some H2O once and a while.
I had a truck that I only used once or twice a year. I had a small panel from Harbor Freight hooked up all the time.
When I sold the truck the battery was 12 years old and still working fine, I even left the lites on for several hours to test it a bit and It still started ok.
I told the friend I sold it to, to get a new battery. I wanted to keep him a as a friend.
He did, so I don't know how much longer it would have lasted with the solar panel hooked up all the time.
I think the panel put out 300ma.
 

Thread Starter

Lumenosity

Joined Mar 1, 2017
470
Good Idea on the solar panel.
What size panel R U using _____ma.
I also agree that you would have to add some H2O once and a while.
I had a truck that I only used once or twice a year. I had a small panel from Harbor Freight hooked up all the time.
When I sold the truck the battery was 12 years old and still working fine, I even left the lites on for several hours to test it a bit and It still started ok.
I told the friend I sold it to, to get a new battery. I wanted to keep him a as a friend.
He did, so I don't know how much longer it would have lasted with the solar panel hooked up all the time.
I think the panel put out 300ma.
Thanks N11778.
I use a 10 Watt panel that PEAKS out at 0.61Amps and 20.1v for the smaller UPS batteries
I've left these out in bright sunlight for weeks with no damage to the battery and the capacity slowly rises over time.
But I have to add distilled water once a week during the process.

Truth Be Told.....I'm not sure it's really worth the effort for batteries that are already way down in capacity as far as battery backup UPS devices are concerned since brand new 12v, 7.2Ah SLA batteries are only about $16.00 shipped.

But for periodic maintenance (clearing suflate buildup before it gets serious) and keeping batteries that are not currently in use topped up solar panels are THE BOMB.

As far as larger lead acid batteries....I think you're right on the money. Connecting a 10 or even 20 Watt solar panel to your car and having it on the dash to keep the battery topped up can make your car batteries last a LOT longer by preventing sulfate build up.

But I would NEVER connect anything more than 20Watts because that's about 1.2Amps
(UNLESS), I was in a pickle and needed to FAST CHARGE a battery. Then I might connect one of my 100 Watt, 6.5 Amps solar panels but only to a car battery and I would monitor the voltage closely with a meter ( and with protective eyewear)
You get about 0.6 Amps for every 10 watts.

As far as my bigger UPSs are concerned (the 24v units), I'm thinking of getting a 24v, 20-30watt panel and running cables to my bigger UPS's to charge them from the solar panel which I would mount on my roof. That way if there's an extended power outage, at least the panels can charge them during the day.

Here's one of my 20Watt Car battery maintainer panels at work :)
SolarCharging_4_20170209_152052 copy_zpseaq5oczg.JPG
 
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Thread Starter

Lumenosity

Joined Mar 1, 2017
470
I received my lead acid battery capacity tester today and immediately put it to work.

Soon found out that the brand new "8Ah" SLA batteries I recently bought are not quite as advertised.

From a fully saturated charge at 13.2v and discharged at 3.00Amps to 11.00v (under load) the capacity was 4.35Ah or just about half the advertised capacity. At 11.00v (under load) the voltage began to drop off quickly so I knew that continuing the discharge would not yield much more capacity.

This is probably VERY common for retail SLA battery backup batteries I would wager.

I'll be running more tests at different load levels and on various batteries. But I'd gamble a bet that you're not getting the run-time out of your UPS because the batteries do not have the advertised capacity (depending on where you got them).
 

Ylli

Joined Nov 13, 2015
1,018
I received my lead acid battery capacity tester today and immediately put it to work.

Soon found out that the brand new "8Ah" SLA batteries I recently bought are not quite as advertised.

From a fully saturated charge at 13.2v and discharged at 3.00Amps to 11.00v (under load) the capacity was 4.35Ah or just about half the advertised capacity. At 11.00v (under load) the voltage began to drop off quickly so I knew that continuing the discharge would not yield much more capacity.
Unless things have changed since I was in the industry, SLA batteries are rated at a 20 hr rate. IOW, you need to load your 8 A-hr battery to 0.4 amps and see what you get.
 

crutschow

Joined Mar 14, 2008
26,374
From a fully saturated charge at 13.2v and discharged at 3.00Amps to 11.00v (under load) the capacity was 4.35Ah or just about half the advertised capacity. At 11.00v (under load) the voltage began to drop off quickly so I knew that continuing the discharge would not yield much more capacity.

This is probably VERY common for retail SLA battery backup batteries I would wager.
Yes, it's common for the reason that Ylli mentioned.

Here's a graph that shows the typical reduction in capacity as the discharge rate increases.
As you can see it's constant until you get to about the 10Hr rate and drops to about 50% at the 2Hr rate.
Your discharge was at the 2.67Hr rate which corresponds to about 60% or 4.8Ah, slightly more than you measured.

 

Thread Starter

Lumenosity

Joined Mar 1, 2017
470
Unless things have changed since I was in the industry, SLA batteries are rated at a 20 hr rate. IOW, you need to load your 8 A-hr battery to 0.4 amps and see what you get.
Ahhhh....
Thanks. I'll try the test again at that discharge rate....although in real life (in a battery backup under 100 - 150watt load) a discharge rate that low will hardley ever be encountered and will almost always be significantly higher.
 

Thread Starter

Lumenosity

Joined Mar 1, 2017
470
Yes, it's common for the reason that Ylli mentioned.

Here's a graph that shows the typical reduction in capacity as the discharge rate increases.
As you can see it's constant until you get to about the 10Hr rate and drops to about 50% at the 2Hr rate.
Your discharge was at the 2.67Hr rate which corresponds to about 60% or 4.8Ah, slightly more than you measured.

Maybe I'm having a derp moment.....
Where did you get 2.67Hr rate?

Thanks
 

Thread Starter

Lumenosity

Joined Mar 1, 2017
470
Crutschow & Ylli,

I did another test run.....same battery but at 8Ah / 0.50A (16Hr rate) and the result was 5.108Ah or about 64% of the expected reseult.

NOW can we say for certain the battery does not live up to it's claim or would I need to do yet a different test?
 

Ylli

Joined Nov 13, 2015
1,018
I'd say it came up short.

Only thing else I can think of that you might try is to cycle it a few time. Believe it or not, the capacity of a lead acid battery increases during it's first dozen or so cycles before it starts dropping again from use and age.

Be sure it is fully charged each time, then take it down to 10.5 volts. (1.75 volts/cell).
 
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N11778

Joined Dec 4, 2015
174
Your lucky to get better than 50%
I have found most all claims are Bunk
Solar panels I have tested run around 50%
Most Electronics (Inverters, Solar regulators) I have tested run around 50% some as low as 20%
 

Thread Starter

Lumenosity

Joined Mar 1, 2017
470
Your lucky to get better than 50%
I have found most all claims are Bunk
Solar panels I have tested run around 50%
Most Electronics (Inverters, Solar regulators) I have tested run around 50% some as low as 20%
Really?

I have a lot of solar panels ranging from 100watts down to 10watts and not one has ever tested below the stated specifications.
Most test about 10-20% BETTER.
Honestly. I test every solar panel I get for voltage max and current max.

Why could your results and mine differ so much?

Or maybe I'm solar naive and not testing them the way you are???
 
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Thread Starter

Lumenosity

Joined Mar 1, 2017
470
I'd say it came up short.

Only think else I can think of that you might try is to cycle it a few time. Believe it or not, the capacity of a lead acid battery increases during it's first dozen or so cycles before it starts dropping again from use and age.

Be sure it is fully charged each time, then take it down to 10.5 volts. (1.75 volts/cell).

Ok..I'll try cycling them a few times. I've heard of that with Li-Io batteries. Didn't know Pb-H2SO4 batteries were like that.
 

MrAl

Joined Jun 17, 2014
7,962
Hello there,

Yes has others have pointed out the discharge rate has to be 1/20 C to test the capacity. That also suggests that a good design target point would be, if you can afford to, to use a battery that only gets drained by 1/20 C in the actual application too. That may require a bigger battery, and again if you can afford the dollars and space.

The reason why you'll see a lower capacity with drawing currents higher than 1/20 C is because each battery has a derating factor associated with it often referred to as the "P" factor. The P factor tells us how much the capacity decreases as we go over the 1/20 C discharge rate. You can find more info about this on the web and i am not sure if you want to be bothered with this or not. It's an exponential relationship and determining the P factor without a data sheet that specifies that would mean doing a few tests which require charging and discharging the battery.
Since you already did one test however, at least you know what to expect now at that particular current drain.
 

dendad

Joined Feb 20, 2016
3,721
I have a couple of large lead acid 12V batteries on solar for my shed ham radio and exhaust fan supply. The plan is to run my whole internet/Ethernet network on solar, eventually.
But I would really love to use Nickel Iron cells. At the moment I cannot afford to buy a stack of them, but it is the plan. The capacity is lower, and the self discharge higher, as is the internal resistance. Another thing that is greater is the LIFE!!
They are almost unbreakable. If you fully discharge them, you just recharge them again. And overcharging and drying them out, just top them up again. I used to work at a shortwave radio transmitter station and there was a battery bank installed there just after the end of WW2. And the batteries were still going strong 50 years later. They are probably still there. As you have a stationary battery, size does not matter much. These are not the best for long range electric vehicle use ;)
The great advantage is extremely long life and often that is not thought of.
It is worth having a look at them I think.
 

Thread Starter

Lumenosity

Joined Mar 1, 2017
470
Hello there,

Yes has others have pointed out the discharge rate has to be 1/20 C to test the capacity. That also suggests that a good design target point would be, if you can afford to, to use a battery that only gets drained by 1/20 C in the actual application too. That may require a bigger battery, and again if you can afford the dollars and space.

The reason why you'll see a lower capacity with drawing currents higher than 1/20 C is because each battery has a derating factor associated with it often referred to as the "P" factor. The P factor tells us how much the capacity decreases as we go over the 1/20 C discharge rate. You can find more info about this on the web and i am not sure if you want to be bothered with this or not. It's an exponential relationship and determining the P factor without a data sheet that specifies that would mean doing a few tests which require charging and discharging the battery.
Since you already did one test however, at least you know what to expect now at that particular current drain.
So would the load for that test be 0.40A ?
 
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