12v/7.2Ah lead acid battery (for computer UPS) drain test

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d_t_a
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12v/7.2Ah lead acid battery (for computer UPS) drain test

I bought a Portalac PXL12072 UPS battery (12v/7.2Ah) sealed lead acid battery from a local shop, but I just noticed the date engraved on the battery seems to be more than a year ago (so it could be 'old stock'). The voltage is still good (12+ volts) when tested at the shop using multimeter.

 

Since I don't have a dedicated sealed lead acid battery charger, I just placed it inside the UPS and let it charge for more than 24 hours (with no load attached to the UPS).  After it was fully charged (I hope more than 24 hours should have fully charged the said battery), I was curious to test its capacity, so I used the EBD-USB+ load tester to test it (set it to 0.2C or 1.20A, which according to the spec sheet lasts around 4-5 hours, with a cut-off voltage of 9.6v or 10.2v -- I'm not sure if I'm reading the spec sheet correctly...)  Spec sheet listed here:  http://www.gsbattery.com/ml-pxl-series/PXL12072    and http://www.gsbattery.com/electrical-lighting-pe-px-pxl-series

 

But anyway, the load/capacity test result graph:

 

Based on the load test graph, is this battery still good?

(I notice the voltage has already dropped below 12.0v at around 3000mAh capacity output.)

I'm not sure up to what cut-off voltage does a UPS designate as 'discharged'. 

From previous batteries - when still in good condition, assuming a load of around 100watts or less, the UPS would last around 5 or so minutes (with the previous batteries, haven't tested it yet with this new one)

(Are the correct terms for the UPS batteries "valve regulated lead acid batteries" VRLA?  How about the proper terminology for the lead-acid batteries for automotive start-up batteries?

Edited by: d_t_a on 10/20/2017 - 12:23
maukka
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I just recently tested an original 12V UPS battery from a cheap APC Back-UPS ES 700G that had been used 24/7 for 5 years. At 1A discharge it had accumulated 4670mAh at 12V. So yours does seem to drop quite fast and the initial drop would indicate quite high an internal resistance too. Mine stabilized at 13.02 volts after a minute.

d_t_a
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That’s what I also thought, voltage seems to be a bit low, although might it also be due to the USB-to-alligator clip I’m using?

I’m using this:

https://www.aliexpress.com/item/USB-Crocodile-wire-Alligator-clips-Male-...

(That store has 2 versions, a thicker shorter version and a thinner longer one — I’m using the shorter thicker version cable for my above EBD-USB+ test. I haven’t tested how much resistance the cable could have introduced to the above test though.)

Enderman
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Loos good, 7Ah.

snakebite
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you could be dropping a lot across the usb clip lead adaptor.
under load measure at the battery and compare the reading to the analyzer reading.

JPLight
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Yes, capacity looks fine. You hardly reach dedicated capacity on lead acid batteries.

Refering to the discharge current I totally agree to what snakebite wrote.

Barkuti
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Fully discharging Pb batteries is harmful for them, even for deep cycle types.

Just a little investment in some LiFePO4 cells can make UPS battery lifespan multiple times longer. It is a long term investment which pays off.

 

Cheers Smile

Tom Tom
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It looks like a very good battery, remarkable to hit specification at that current. Usually they are specced at 20c rate.

Look after it. And don’t test it again. (every total discharge counts, more than a hundred over life would be great)

And don’t listen to the naysayers who do not understand the point of standby/ups etc. applications, where these things are basically never expected to be used, and to sit on float throughout their lives, waiting for the few times in their lives that they are needed. Or a monthly check, if serious about things. Arguable whether it is better to test frequently, or just do scheduled maintenance.

Lead-Acid still does this best, sealed AGM cells particularly.

Unless you expect to use it frequently, in which case you might want to re-think entirely your strategy. Which would definitely not be to use e.g. an off-the-shelf UPS instead of a calculated battery bank, charger, inverter, solar panels etc.

Get to know an industrial UPS service company and you might get an unlimited supply of good-as-new batteries for scrap price Wink For e.g solar off-grid use.

d_t_a
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Barkuti wrote:

Fully discharging Pb batteries is harmful for them, even for deep cycle types.


Just a little investment in some LiFePO4 cells can make UPS battery lifespan multiple times longer. It is a long term investment which pays off.


 


Cheers Smile

At what voltage is considered “fully discharged” for a Pb battery?

So, since I’m doing the above test as a “benchmark reference” in the future, will doing similar above test (once or twice) reduce the max capacity or cycle life by significant amount (eg. 1-2% max capacity or cycle life reduced by doing above draining test)?

Barkuti
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BU-903: How to Measure State-of-charge @ Battery University

 

 

d_t_a, just recharge your battery and be our guinea pig. Smile

In my experience, I know deep cycling UPS batteries (high current draw) is a killer.

 

Cheers Party

DoubleA
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About the cycle life it depends on the battery and the manufacturer. What cycle life was advertised for your battery at 80% DOD?

Also the runtime your UPS can depend on the type of circuitry and it’s efficiency. I’ve used real crappy ones with really low Power Factor and they lasted only about 2 minutes even though my battery was capable of providing power for more than 20-30 minutes or so.

Barkuti wrote:

Just a little investment in some LiFePO4 cells can make UPS battery lifespan multiple times longer. It is a long term investment which pays off.

It’s a good choice but then he would have to use a balancer circuit for those.

and on the first day he said "Let there be light"...

Barkuti
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DoubleA wrote:

It's a good choice but then he would have to use a balancer circuit for those.

No real reason to do it if you use a pack of consistent, quality cells. Cell balance could also be a problem with Pb batteries. Also, 4S balancing circuits are cheap as chips. 

 

Cheers Party

d_t_a
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Barkuti wrote:

BU-903: How to Measure State-of-charge @ Battery University


 



 


d_t_a, just recharge your battery and be our guinea pig. Smile


In my experience, I know deep cycling UPS batteries (high current draw) is a killer.


 


Cheers Party

Yup, being a guinea pig in the name of scientific research. Wink

I hadn’t checked what’s the “resting voltage” (ie. unloaded voltage after resting 2 hours)… maybe when I do another test, I will do that.
The voltages taken by EBD-USB+ is the loaded voltage, so there’s a voltage sag due to the current load.
Also, after taking off the load at the cut-off voltage, the resting voltage is still rising, but I hadn’t taken time to record them in my test.

~~~

I did a different test of the battery (actually, I tested the older battery I’ve been using, which is also a Portalac, but higher model PXL12090, tested while installed in an APC Smart-UPS 420 (this is a very old model that I got as a refurbished unit for backup purpose), I position the battery so I can use a multimeter to check the voltage of the battery while it’s in use.

What I noted:
(old but still working) Portalac PXL12090 on APC Smart-UPS 420: used a 20-watt LED bulb as a constant load (connected to a ZhuRui PR10 power recorder to check the wattage, which seems to start as high as 21.0 watts but much later goes down to 18.6 watts)
with the said battery, I pulled the plug from the electrical outlet, then I checked the voltage manually, ie. read the PR10 power meter reading and checked the battery voltage while loaded (at irregular intervals, since it’s manual)

27 minutes 8.68Wh (PR10 reading of power consumption with only the 20-watt LED bulb)
55 minutes 17.46Wh (hadn’t tested the battery voltage)
01:07 21.35Wh
01:33 29.35Wh 11.75v (this is using my multimeter, while the battery is still inside the UPS, under the 20-watt load)
01:49 34.32Wh 11.51v
01:58 37.22Wh 11.26v
02:03 38.65Wh 11.04v (the UPS started its “fast beeping” sound at this time to indicate “low battery condition”)
02:06 39.37Wh 10.72v
02:07 39.79Wh 10.60v
about 2 minutes later the UPS automatically shutdown (unfortunately I wasn’t able to get the exact reading during the shutdown)
however, about 5 or maybe 10 minutes after the automatic shutdown of the UPS, I checked the voltage of the battery (still installed in the UPS, off), it was 11.65v <== so this is the “rest voltage” but only after 5-10 minutes (not 2 hours as per above table)

(my Mastech MS8229 multi-meter seems to have ill-calibrated readings, I notice it may be 0.02v higher reading when testing Li-Ion batteries; not sure what’s the error when measuring around DC12v)

conclusion: with a 20-watt AC load on the UPS, the 12v lead-acid battery Portalac PXL12090 was able to power for a bit more than 2 hours, which is nearly 40Wh of power.

(I also did a drain test of the old PXL12090 and its capacity is only slightly lower than the new PXL12072)

d_t_a
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My 5-year old PXL12090 (currently installed and used inside an APC Back-UPS CS 500 (BK500EI)

Seems to still have pretty good capacity >6000mAh (I think I bought it and started using it sometime 2012).

So, with 20-watt AC load on the UPS, it drained the PXL12090 battery in about 2 hours (2-hour discharge rate), giving around 40Wh (based on PR10 power recorder’s consumption reading).
(my last noted voltage check is 10.60v while under load in the UPS, my guess is the shutdown voltage is somewhere 10.45v loaded voltage)

While using EBD-USB+ at a 5-hour discharge rate of 1.20A, it gave around 75Wh (10.20v cut-off voltage).