Unexpected SLA Battery behavior.

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,467
6-FM VR Sealed Lead Acid Battery
12V/20HR

Comes out of one of those car battery boosters you keep in the trunk. Me, personally, I know that they need to be charged about every 3 to 4 months or the battery will go bad. Not dead - BAD. I've given these things to friends and family and specifically told them they need to charge them regularly - even if they haven't been used. Got this one back a few days ago and have been playing with it. First thing I did was to remove the battery and put it on a charger. Charge went up to 14.2V rather quickly, then settled down to 13.6V. Took it off the charger and let the battery sit for a few days without any charging or without any loading. Battery voltage stayed around 12.7V, which from what I know about Lead Acid batteries is a pretty good sign.

Completely disassembled the battery booster and hooked things up and checked the charging characteristics of the booster control board. The battery again quickly reached 14.4V and the charge cycle shut down. Thinking maybe the battery is ok, I know, foolish assumption, I connected a 12V 1.4A computer fan to the battery. Voltage began to fall quite quickly. Within 2 minutes it had fallen to 9.29V. But running all the time I've been typing (60+ WPM) the fan has been running and the battery voltage has climbed at present to 10.12v. I don't understand why the battery voltage is climbing again. Am I de-sulfating the plates? What will happen if I continue to run the fan for an hour? I know, "Test". However, all I can test for is voltage, and assume the current being drawn is 1.4A.

The battery is completely disconnected from all electronic circuitry, other than connected to my meter and the fan. At present the voltage briefly is showing 10.14V. Will this battery recover if cycled a few times? Or is it just plain useful as a door stop?
 

crutschow

Joined Mar 14, 2008
28,227
I don't understand why the battery voltage is climbing again. Am I de-sulfating the plates?
Not sure.
I think you can only de-sulfate the plates when it is charging.
Will this battery recover if cycled a few times?
Worth a try.
The battery should go to about 14.5V when it is on the charger and fully charged, unless you have a smart charger (which I suspect if the voltage dropped to 13.6V with the charger connected).
For a smart charger leave it on the charger for a day or so.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,467
I used a regular battery charger initially just to get the voltage back up so I could see where it sat. Then, after disassembling everything and setting it up for a bench test, using the charging circuit in the battery booster it quickly went up to 14.2V then shut down. It said the battery was fully charged. I unplugged the booster and plugged it back in and again, it almost instantly hit 14.2V and shut down.

It would be nice to recover this battery if possible, but the main thing I'm after from the booster is the electronics. I want to connect it to a stationary 12V Lead Acid (wet) battery and leave it plugged in. What I hoped to discover is whether the charger will come back on by itself or if I need to cycle the main power. But that's not the purpose of this thread; it's to understand what's going on with the battery.

The fan has been running all this time and the voltage is now at 10.26V. I'm just at a loss to understand why a battery will start showing higher voltage while under load. Perhaps I should try a higher current load and see what happens. Will have to find something else to connect.
 

dl324

Joined Mar 30, 2015
13,574
Will this battery recover if cycled a few times? Or is it just plain useful as a door stop?
I've had little positive experience trying to rejuvenate SLA's.

The battery maintainer I mentioned in another thread also has a restore function. I think it's applying some high frequency pulses to the battery because I can hear it whining. If the restore function doesn't think it's making any progress after an hour, it indicates the battery is bad.

I had an Exide wet lead acid battery for my riding mower that wouldn't hold a charge and the restorer seems to have revived it. It sits on my garage floor and is holding a charge for several weeks or more. When it was in my mower, I had to jump start every time I wanted to use it. The battery restorer indicated that this battery was bad, but after several attempts with the restorer and a regular battery charger, it has recovered some usefulness.
EDIT: added wet lead acid.

I tried it on some 12V SLA's from UPS's and it couldn't rejuvenate any that I tried. They were in an uncharged state for so long that there's no chance of removing enough sulfation to let them hold a charge.
 
Last edited:

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,467
Sounds like a cell is shorted.
I don't know. It DID have a battery voltage of 12.7 volts after sitting for a few days. Now, I don't know all there is to know about batteries. But after disconnecting the fan the voltage went up to 11.25V. So I connected it back to the booster charger circuit and started getting odd flashing lights. However, the lights have settled down and are now showing a progressive charging going on. At present, no fan, just the booster circuit, the voltage is up to 13.53V and climbing. I'll do this a few times to see what happens. I may even run the fan for a longer period of time; or connect a heavier load to the circuit.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,467
Moments ago the booster said the battery is fully charged. I'm now running the fan AND the booster. Seems to be maintaining a voltage of 10.8V. The booster came back on when voltage dropped. I can't say how low the voltage dropped before the booster came back on, things happened faster than I could look two different places.

[edit] nope. Voltage is still dropping. Now down to 10.71V
 

dl324

Joined Mar 30, 2015
13,574
Voltage is still dropping. Now down to 10.71V
I think you're going to need to try a battery restorer. A charger just applies a voltage. A restorer will try to use high current pulses to break up the sulfation. I'm using a Harbor Freight model. I'm so happy with it's performance that I'm going to buy several more the next time they're on sale and connect them to the batteries in vehicles that aren't being driven.

1633887179593.png
This unit will do sealed and wet lead acid, 6 or 12V. It has a special winter mode.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,467
Thanks dl324. I'll have to make a trip to HF one of these days.

However, I am more interested in the charge controller circuit inside the battery booster. After several cycles it looks like the boost charger will come back on when the voltage drops to 12.7V or thereabouts. Restoring the battery is just a bonus if it can happen.
 

MisterBill2

Joined Jan 23, 2018
9,908
Strange behavior?? YES! several years back I returned from a mid January plane trip to find a buried car in the long term lot. After gaining access I tried to start it so it could warm up while I finished digging it out. I got about three turns and no more. So I continued digging it out until I would be able to use jumper cables to get it started. But after finishing I climed in and gave it another try first. IT spun up and started and after letting it idle for a minute I backed out and headed home.
My guess is that the first effort created enough heat to make the battery come to life. What other explanation would there be? It had been a very cold week while I was gone.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,467
@MisterBill2 I've heard of that sort of thing before. Heard that when very cold, you turn the headlights on for a few minutes to warm the battery, then start the car. However, this battery has been in my lab for some days. Certainly long enough to climatize to the ambient temperature. Overnight it was 63.7˚F and warmed to 76.6˚F. At present it's 68˚.

As per
I think you're going to need to try a battery restorer. A charger just applies a voltage. A restorer will try to use high current pulses to break up the sulfation. I'm using a Harbor Freight model. I'm so happy with it's performance that I'm going to buy several more the next time they're on sale and connect them to the batteries in vehicles that aren't being driven.

View attachment 249948
This unit will do sealed and wet lead acid, 6 or 12V. It has a special winter mode.
I went out and bought one. Cost me $37.99. Sign said normal price was somewhere in the $40 range (US). Have the battery on the charger now. But now there's a new dilemma; the charger voltage indicator is a good 300mV different from my high tech, very expensive "Extech" meter. Don't know which to trust less.

Back when I used to work next to the metrics lab I used to bring my meters in for calibration. Well, those days are very long gone and I don't know what to think of this. Perhaps I should start up my scope and see because the voltage is fluctuating between 13.8V & 14.3V in rapid succession. Perhaps that's the high frequency thing whereas the Viking charger is fluctuating between 14.0 & 14.7V. Of course I haven't read the instructions yet. Not that I ever will - I'm a guy. And guys don't read instructions. Am I right?
 

dl324

Joined Mar 30, 2015
13,574
But now there's a new dilemma; the charger voltage indicator is a good 300mV different from my high tech, very expensive "Extech" meter. Don't know which to trust less.
I'd trust the battery maintainer more.. It's voltage varies and your Extech is going to do some sort of averaging.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,467
OK, scope seems to agree with the Viking. Showing 14.0 to 14.4 volts sweeping up and down but surely not at a high frequency, more like it's varying between the two voltages at 2Hz.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,467
Pg. 6 briefly covers setup, pg. 7 covers operation, all six lines of it, pg. 9 covers hookup and what symbols mean what. Out of 11 pages.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,467
Already a green light with no indication of a bad battery. However, running that fan for 3 minutes has dropped the voltage into the 10V range. Clearly a 20Ah battery shouldn't drop off that fast.
 

dl324

Joined Mar 30, 2015
13,574
Already a green light with no indication of a bad battery. However, running that fan for 3 minutes has dropped the voltage into the 10V range.
It may take several charging cycles. I had to charge my mower battery with a regular charger several times before the restorer could work it's magic. I had nothing to lose because the battery was out of warranty. They're unbelievably short these days. I think mower batteries are only 3 months.
 

crutschow

Joined Mar 14, 2008
28,227
Still sounds like a shorted cell.
That would give a voltage about 2.1V below the nominal 12.6V (or 10.5V) for a 12V SLA battery, which is about what you seem to be experiencing when the battery is under load..
It's unlikely any type of "restoring/conditioning" will correct that.
 
Last edited:

MisterBill2

Joined Jan 23, 2018
9,908
Not a shorted cell, but a dried-out cell. And it might work to add some water. Some gell-cell batteries can be opened by very carefully removing the cover over the vents and then pulling out the rubber vent plugs. On some I have been able to add water and get them back to working some. It is a tedious process and it does not always work, but sometimes it does.
 
Top