I know this isn’t going to be a particularly flashlight related question but there are a lot of knowledgeable people here so I hope someone can help.
Recently I discovered a pile of sealed lead acid batteries in the corner of the stores at work.
Nobody knew where they had come from or how long they had been there but I was told if I wanted them I could have them.
The batteries were mostly Ysasa NP7-12, 12volt 7Ah batteries and as they were physically stuck together in pairs I think more than likely they have come out of some UPS units.
There was also a few larger NP38-12, 38Ah batteries and a couple of these were still in sealed but old looking original cardboard boxes.
I wasn’t going to be able to take all the batteries with me that day and if they were completely dead I wasn’t going to take them at all so I put a volt meter on them and read the voltage.
The best 3 pairs of the small 7Ah batteries read 12.5+12.3, 12.5+11.5 and 12.3+11.0 volts
The best 2 of the larger 38Ah batteries read 11.7 and 11.5 volts.
So the above batteries are the ones I took home but there were others reading various voltages all the way down to about 5 or 6 volts.
So finally to my questions
Is a voltage reading in away an inducation to the health of these batteries?
Are any of the lower voltage batteries I left behind worth having?
My intended use for these batteries is for a couple of APC uninterruptible power supplies.
Voltage readings indicate good battery condition. 12.5V ~ 12.6V mean fully charged. ~12.2V around 50% state of the charge.
I guess they all in good health if they didn’t removed from UPS units.
Here another way to get an idea of battery health - load test
Find 12V automotive head lamp bulb (55W/60W)
If battery can fully illuminate bulb, it in good health.
Some aged (specially used) batteries show correct open cell voltages but failed under load.
Don’t bother with the low voltage ones. They are probably sulfated up and not worth messing with. Run most SLA batteries down and they die. They particularly don’t like a slow and agonizing long term storage self discharge death.
Once a battery sulphates up, they are never quite the same. It is a lot like zapping nicads to cleat shorts… works for a while, but damage has been done and problems are very likely to come back.
Also most SLA batteries use a gelled electrolyte. There are a lot more sensitive to sulphate damage than wet batteries. The gel dries, shrinks, cracks…
Meaning that you actually apply
8-9V + ( Resistance of Battery / .050 )
If we assume 20 milliOhms Internal Battery Resistance and 8V resting voltage
8 + (.020 / 0.050 ) = 8.4V
It would take a LOT of current to apply 30V to a SLA battery.
PPtk
P.S. No, this doesn’t take every factor into consideration, but it’s a rough estimate of the voltage required to apply a given charging current to a battery.
Having used the NP7-12 in many UPS (APC,Compaq, HP) they will take a real beating from deep discharge and still come back. On average 4-6 years heavy use. have seen 6-8 years on conditioned packs. Conditioning with weekly discharge re-charge cycles from the UPS
The small ones also are used for alarm backups. And Yuasa make rather good motorcycle batteries too.
If they’ve been in a UPS they are most likely totally useless. Like already said, if it won’t light up a 12V bulb of decent wattage, recycle them. The batteries in the UPS here can produce their rated output for around 3 seconds which is not exactly helpful for anything.
I have a number of these very same batteries, some cane from UPS units and some came from jump starters. The jump starters were new but I let them sit to long without keeping them charged up. Do the desulphators that I read about not work. I have both hesitated to throw them out for fear that they can be rescued, and hesitated to get a desulphator out of fear that they do not work.
They work better on wet-cell batteries than on gel cell (SLA) batteries. There’s much more electrolyte mobility in a wet cell like a typical car battery.
Put them on a charger and see if they accept a charge. You can use a bench supply at 13.7V to charge as well. Current limiting isn’t an issue, the battery will only accept just so much anyway (maybe keep it under 5A though). If you have a Lead Acid smart charger, use that since it will do a boost charge (up to 14.4V) to start, which helps to balance the cells.
We used to use a lot of these at work, and rotated them through use so they would last longer. leaving them to sit without topping up is not good for them. We did a quarterly rotation. Anything still showing above 11V has a chance at being useable. A load test will give you an idea if they are dried out or have a weak cell.
So far I have fitted the best pair of NP7-12s to an APC UPS.
It powered a 60 watt light bulb for 23 minutes, new batteries powered the light bulb for 1 hour 27 minutes.
So they’re well down on new batteries but still worth having as they’ll provide enough time for the PC to do an orderly shutdown.
APC will advise that storage is limited to 6months without a charge. The NP7-12 will be useful in a UPS for approx 4 years (temperature is usually the biggest factor).
The NP7-12s will not last as long as the np38s, these are probably 10 year design life, in a UPS application, 6-8 years.
If you use old batteries you may find the UPS goes into alarm, if ignored the batteries can over heat and expand. The pairs can actually become welded together by the cases melting. They may also expand enough to wedge themselves inside the unit.
Recovery by any means will not give good results.
Regular discharge of these specific ‘standby’ batteries will damage them. 1.65 Vpc is probably as far as you should take them, below that damage is done.
These batteries are not too expensive, iirc around £15 each.
