6 volt battery sitting at 1.47 volts. Can it be charged?

Thread Starter

Tonyr1084

Joined Sep 24, 2015
4,539
This is a SLA battery, 6V 1.2AH. Been sitting on the shelf uncharged and unused. At the moment I have it connected to a 5 volt supply. Am I wasting my time? It is my later intention to put it on a 6 volt battery charger, but that's bulky and kept in the garage. Also has the big bulky jumper type battery clamps, so I'll have a hard time connecting this tiny battery.

Am I wasting my time? As mentioned, the shelved voltage was 1.47 volts. I want to see if a 5 volt regulated power supply (36 amps) can put a little juice back into this battery and make it chargeable and useful.

(battery case temperature is 74.5˚ F or 23.6˚ C) (I wish I had a 6.8 volt supply)
 

AlbertHall

Joined Jun 4, 2014
9,875
Time will tell. I expect the current will be very low but don't be tempted to take it above its normal charging voltage to get more current. Go make yourself a nice warm cup of patience.
 

crutschow

Joined Mar 14, 2008
24,978
As Albert noted, it likely will take time, several days or more for it to recover (if it will).
But limit the current to no more than about 1/10th the AH rating.
 

iONic

Joined Nov 16, 2007
1,650
Take the advice of your first two responders. With a little luck, you may have a battery that will function, albeit not likely optimal. It definately has taken a hit due to sulfation.

Causes of battery sulfation:
  • Batteries sit too long between charges. As little as 24 hours in hot weather and several days in cooler weather.
  • Battery is stored without some type of energy input.
  • Undercharging of a battery to only 90% of capacity will allow sulfation of the battery using the 10% of battery chemistry not reactivated by not completing the charging cycle.
  • Low electrolyte level - battery plates exposed to air will immediately sulfate.
  • Incorrect charging levels and settings. Recommend a 3-phase charge cycle (Bulk, Absorption & Float) and a charge rate equal to 10% of the C20 (20 hr AH rating) of the battery bank.
  • A battery sitting for extended periods in a partial or discharged state is more likely to retain a build up of sulfation, which hardens and is more difficult to remove through equalization's.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
4,539
Causes of battery sulfation:
  • Batteries sit too long between charges.
  • Battery is stored without some type of energy input.
Battery has been shelved for a few years uncharged. It came out of a home security system, it's the backup power battery. The security system is unused and unwanted. The battery MAY be of some use though. So I saved it. The other day I decided to check the charge and found it sitting as low as mentioned. If the battery doesn't recover - oh well. No loss to me. Just a shame to waste an otherwise (what could have been) a good battery.

@AlbertHall
@crutschow
@iONic
Thank you gentlemen for the guidance. I'll limit it to 0.12 amps. 5 volts divided by 0.12 = 41.6Ω (47Ω) to be safe.

Incidentally, the battery case temperature has not changed. Good sign I'm not going to burn down the house all for the sake of a 6 volt battery.
 

iONic

Joined Nov 16, 2007
1,650
If you can get this old guy charging it should be fully charged and floated at about 6.75V. The 5V charging supply will only get the battery to the fully discharged state. Your battery, if you don't mind me saying, is currently in the "dead" state.
 
Last edited:

thedoc8

Joined Nov 28, 2012
147
Look into the cells to see how much junk is on the plates. The top of these batteries will pop off and will have little covers on each cells that will also pop off. I have never had any luck with the recovery. We use a few hundred of these batteries. Two years on the shelf seems to trash em. Time will tell
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
4,539
Look into the cells to see how much junk is on the plates. The top of these batteries will pop off and will have little covers on each cells that will also pop off.
I have done that in the past but have not really been able to see much in the way of condition. Keep in mind this is a small battery.
What's it doing now?
Yesterday at the advice of Crutchow I put a 47Ω resistor in series with the charge (at 5 volts). I noticed the disconnected voltage of the battery (not hooked to the charger) was 1.73 volts. This morning the voltage is largely unchanged. I have just a moment ago removed the resistor to let the battery pull as much as it wants. It isn't looking good for this battery. After being on a charge since yesterday I had hoped it would be above 2 volts. But when I first started charging the battery I managed to get it from 1.4 to 1.7 volts in a few hours without the resistor. So I've removed the resistor. Let's see if that does anything positive.
 

AlbertHall

Joined Jun 4, 2014
9,875
After being on a charge since yesterday I had hoped it would be above 2 volts.
You're not in any hurry to use this battery. The amount of electricity it is consuming is negligible (and hence why nothing much is happening).
Just put it by the coin cell experiment and let it run.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
4,539
the voltage is largely unchanged.
By that I mean 1.73 volts became 1.74 volts. 1/100 of a volt in over 24 hours means a VERY slow charge rate. But then again, it's a 6 volt battery and I'm connecting it to a regulated 5 volt source. I don't expect much to happen to it. Maybe today I'll stop by Xfinity (a cable provider in the US) and grab one of their used 12 volt wall wart (power bricks) and modify its reference voltage so that it outputs 7 volts (6.8 is a good float voltage for a 6 volt SLA). I've modified them before. Took a 12 volt and modified it for 13.8 volts to use as a battery keeper in the garage. Keeps an older car battery charged up for use with an old car radio.
 

AlbertHall

Joined Jun 4, 2014
9,875
If you have something available, measure the current. It should gradually increase and then fall again then it's got as good as it's going to get.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
4,539
Odd habit: When connected to the power source I'm reading 4.95 volts. When I disconnect the alligator clip the voltage drops to 1.6 volts. But if I hold the meter on the battery for a few seconds the voltage starts going up. No, I'm not reverse voltage setup. When I check the voltage and polarity I get +5.11 volts without the battery connected. Connected I get 4.95. When I disconnect from the supply the battery voltage changes to 1.6 volts initially but then the voltage climbs. I've NEVER seen a battery do that before.

I'm currently measuring 5.6 mA (0.0056 A). Seems quite low. Probably an indication this battery isn't going to come back. But then again I'm only pushing 5 volts at it. Will have to look at my collection of wall warts. I have some 9 VDC WW's. Thinking I might have a 6 VAC WW somewhere. If worse comes to worst I could always set up a variable power supply, but I'm trying to keep this as simple as possible so I can ignore it.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
4,539
Today the battery voltage when disconnected from the charge is 0.8 volts. That's going the wrong way. This battery is likely toast. Since it's not highly needed - it can go in the recycle bin at the hardware store.
 

AlbertHall

Joined Jun 4, 2014
9,875
Today the battery voltage when disconnected from the charge is 0.8 volts. That's going the wrong way. This battery is likely toast. Since it's not highly needed - it can go in the recycle bin at the hardware store.
Eeerrrmmm….
Are you really, really sure that you have the polarity correct <ducks and runs away>.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
4,539
Absolutely sure. The red potted battery terminal with the red meter probe plugged into the red probe plug on the meter - I get a positive voltage reading. When I reverse my meter leads I get a negative reading.

Don't have a clue what's going on here. But I DID discover I have a 20VDC power supply. Don't know its amperage though.
 

Norfindel

Joined Mar 6, 2008
326
5v to charge a 6v SLA battery? You need to use 2.3 to 2.35v per cell, so that's about 7v to charge it. Limit current to 1/10th of the AH rating.
Still, leaving a SLA battery uncharged and abandoned for years is a sure way for the plates to sulfate badly.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
4,539
PS is from a computer. 3.3 V; 5.1 V; (-12) & 12 V sources.

As mentioned I discovered a supply I have is a 20 V supply. 20.5 unloaded. Was thinking I could series a 12V battery with the 6V battery. 13.8 float charge plus 6.9 float equals 20.7 volts. I know this little supply won't manage that much voltage, but it's closer to the 6.9 volts (plus the 13.8) than a 5 volt supply.

Was inspecting the 6V SLA and noticed slight bulging on the bottom of the battery. I would have expected to see bulging on the sides before the bottom. But the bulging is minor.
 
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