Regarding typical 12V 9Ah (or 7Ah) SLA batteries used in UPS units:
1. Can they be used upside down?
Some sources say they can be used in any orientation due to being "sealed", while others (eg. a SLA retailer) said they can be used in any orientation except upside down. Incidentally, the CyberPower CP1500PFCLCD takes two SLA batteries, with one oriented right side up and the other upside down. The batteries have failed the unit's self-test after 5 years. A check with a battery tester (Ancel BA301) reports the right side up battery as good with 19mOhm internal resistance (typical spec for SLA), and the upside down battery as bad with 75mOhm internal resistance. Coincidence, or possible cause of failure? And/or bad UPS design? (APC's equivalent units have both batteries oriented sideways.)
2. If one out of a pair of batteries fails, is it ok to replace only the bad battery as long as the internal resistances of the pair are ok/matched, or must they be replaced in pairs?
3. Many sources say SLA batteries deteriorate with age, but how? Another UPS has a 2-3 year old replacement 12V 9Ah SLA that now lasts only about 20% as long as the original 7Ah battery for the same load, but the battery tester reports it as a good battery with low (~22mOhm) internal resistance.
4. Thoughts on adding distilled water to SLAs to revive them? If so, which batteries would be good candidates? (high internal resistance failed battery, and/or low internal resistance but low capacity battery) Lots of people/videos report this can work, others say it provides marginal and unreliable improvement. I wonder about how much water to add without diluting the acid too much, if that even matters. Also, how to know what the source of the weakness is, and whether water will address it.
5. What is proper maintenance for SLA batteries? All of the batteries are kept fully charged in UPS units, so not stored discharged. All of the batteries, including the failed one, show full voltage ~13.3V.
Hi,
In your application how often do the batteries actually have to supply current (and thus power) to a load, rather than just be maintained at the proper float voltage? This would be interesting to hear about i have dealt with these batteries too in the past and a little now too.
What i can tell you is that the batteries do go bad after some years, and i dont think there is any way around that. I think manufacturers collect the cores so they can use the raw materials over again, such as the lead. They probably melt them down and use that metal for new batteries.
I had an older Fios wall box that used a 12v 7AHr battery (much like the 9AHr type) and it would run down after about 2 or 3 years.
There seems to be no good way to revive these batteries once they become bad. Adding water probably would not do anything because i've read that sulfur is not water soluble, but does work in wet batteries to replace lost water due to evaporation. I've read about all kinds of stories where users tried different methods to revive, such as extreme overcharging. Others tried to "clean" out the inside of the battery by dumping all the fluid, then replacing the fluid with a solution, then dumping that, then putting the original fluid back in. That did work, but the tests done afterwards were at low current which says nothing about the true state of health. The ones that had to produce high current that a LA battery would typically have to do never worked. They tried various solutions and nothing worked.
The light current applications did work because as the internal resistance goes up they can still provide some current, but not at the original voltage because the voltage sags. For example, i have a 12v 7AHr battery that i can still use to run LEDs even though it is probably 15 or more years old. That's because there are only two LEDs in series and the current is less than 10ma. They are dimmer now than they used to be though, because the battery is so old now. When it was just 10 years old though the LEDs were still bright and i used it as an emergency storm light and it would run for 24 hours a day 7 days a week, although the longest stretch i ever had to use it for was about 4 or 5 days.
Lead acid batteries have a limited lifespan, and a limited charge cycle life that's why i asked about the way the batteries were being used. The cycle life is very short relative to other battery chemistries, the only advantage i think is that they can supply a large current without having a problem.
The newer type batteries are the LiFePO4 type as they have a much larger cycle life, upwards of 500 times. They have to be oversized though for something that has to supply a high current. They are very lightweight though when you pick up a 12v 7AHr battery it feels like a feather compared to a lead acid battery. Unfortunately, you can not replace UPS batteries that use LA type with the LiFePO4 type as the charge regime is much different and so is the loading specifications. It would not only not work, it could be dangerous. I dont know if you can mod it to work with those type but i would bet you cant use the same size battery you would probably have to go 2 times higher in capacity to get that kind of current without a problem. It would be a serious mod too you'd have to test very carefully so i cant recommend this kind of mod.
As i was saying, in lighter current applications you can overcharge slightly and get more life out of the battery, but that means a different kind of charger or charge manually, and i dont think you can get the capacity you need for a UPS that way either. UPS systems are very demanding so the wise buy systems that are much higher rated than they actually need, as much as 400 percent higher. That means if you need 10 minutes then buy a system that will give you 40 minutes. If you need 10 minutes and you buy a system that can handle 10 minutes you could end up getting 1 minute because that will tax the batteries a little too much.
In the end what most people do is just bite the bullet and buy new batteries when needed. It's a bitch but any other way just doesnt seem to work. We can be happy that at least we have these batteries, imagine life without them. As time goes on we may see better batteries that can take the place of these noble devices as there is a lot of battery research going on mostly due to the continuously growing EV market. It takes a long time to get to market though so we just have to wait patiently.
Just to note, i have never heard of an application where the sealed LA battery was mounted upside down.
I have seen one application where the sealed LA battery completely dried out. I actually took it apart to find out what happened and it was completely dry inside.
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