SLA, Does this sound right?

Recently my wife's wheelchair batteries (1 year old) vented and expanded so we needed to replace them. I didn't take a final voltage reading before we recycled them. We've been using and currently are using the stock charger which is at least 8 years old.

We bought a pair of equivalent 12V 11Ah SLA AGM batteries made by UPG (UB12120). One of the batteries came at 12.9V and the other at 13.0V.

The initial charge took about 40 minutes and brought them up to 13.51v and 13.35v. The next five charges equalized them out to within .01V. The voltages over all six charges ranged from 13.51-14.10 V on one battery and 13.35-14.09 V on the other. The charger LED light went green on the first charge which indicates that it is complete after 40 minutes. Each subsequent charge we've removed the batteries before the charger turned green which was 3-4 hours. We did this because one of the times I could hear bubbling from the battery and we could smell hydrogen gas each time. One of our concerns is that the batteries that we replaced were overcharged so we don't know whether the charger and the replaced batteries are defective.

1. Is there a way to determine if the charger is working correctly (bulk, absorption, float)? I have access to a DMM but I'm unable to find anything on the internet that is helpful.
2. The datasheet for these batteries state that the "cycle use (repeating use) voltage is 14.5 - 14.9 V. Does this mean that it should charge to this voltage to be "full?"
3. The datasheet states that the "float use control voltage" is 13.6-13.8 V. What does this mean?
4. I understand that to prolong the life of these batteries they should not be discharged below 50% but I've seen various voltages for this 50%. Is there a definitive 50% voltage? If not then how would I calculate it for these batteries?
5. The datasheet has a chart that shows "open circuit voltage vs residual capacity" with the range being about 11.5-13.25 V with 11.5 V being 0% capacity and 13.25 being 100% capacity. I assume that this is the resting voltage after 8 hours or so. I have not been able to take a resting voltage so is there another way to use this chart to estimate capacity?

We thank you for any help you can provide.

I did a quick search and it would appear that SLA AGM batteries are of a deep-cycle (ie: non-starter) design.

http://batteryuniversity.com/learn/article/lead_based_batteries

Based on information in the article these batteries are design with a valve to release gases under strenuous charging and discharging. It sounds like your charger is stressing the batteries too much - possibly too high a charge current. I would seek out a new charger which is appropriate for your capacity batteries.

I don't know more to pass on further on these types of batteries, but I am sure others with more knowledge will be able to help further.

TY ShineOnYouCrazyDiamond. We saw that page but were not able to answer our questions from it. We're thinking that the charger should probably be replaced but we'd still like to know so that it can be operate correctly and get the best use of the batteries.

ACruceSalus said:

Recently my wife's wheelchair batteries (1 year old) vented and expanded so we needed to replace them. I didn't take a final voltage reading before we recycled them. We've been using and currently are using the stock charger which is at least 8 years old.

We bought a pair of equivalent 12V 11Ah SLA AGM batteries made by UPG (UB12120). One of the batteries came at 12.9V and the other at 13.0V.

Click to expand...

Sounds more like a small shopping scooter than a wheel chair, that's a very small battery for a wheel chair.

Norm

Norm that's correct. It's a GOGO Elite mobility scooter but it's all she has to use at this time.

ACruceSalus said:

Each subsequent charge we've removed the batteries before the charger turned green which was 3-4 hours. We did this because one of the times I could hear bubbling from the battery and we could smell hydrogen gas each time.

Click to expand...

Hydrogen gas is odorless, so you must have been smelling something else. Hearing some quiet bubbling during the final stage of charging is normal. If it's hissing or venting, that's a problem. Does the battery still feel cool to the touch? If so, it's probably fine. If it's hot, then the charger is boiling it which is bad.

Nearing the end of charging, your charger should be putting in around 0.5 amps or less. Hopefully it's a smart charger designed to cut back current as the voltage rises and it detects the battery is mostly charged. If it's not working, then perhaps it is putting in too much current and that's why it's boiling.

I understand that to prolong the life of these batteries they should not be discharged below 50% but I've seen various voltages for this 50%. Is there a definitive 50% voltage? If not then how would I calculate it for these batteries?

Click to expand...

Preferably keep them above 70%, but 50% is okay too. For an AGM battery, a resting voltage around 12.3v or 12.4v is probably around 50% charged, but check with the manufacturer because it varies. It's always best to keep a SLA battery topped up to full charge, so go ahead and charge it whenever you can. As long as your charger is working properly!

Possibly smelling H2S or some other sulphur compound.

I also suspect the charger.

I have searched and found many tables for State of Charge for AGM SLAs and they seem to be all over the place (voltage wise) for 50%. I tend to operate on the conservative side, not going below 12.50v (with the battery in a resting state) under anything but an emergency.

I have a few 12180s a couple 12100s and a 1250 that I use for testing small devices. My Battery Tender Jr has served me very well but I have not seen a BT charger in 24v.

Hello ACruceSalus,

I would suggest replacing the 8 year old charger with a charger specifically designed to charge AGM batteries. It sounds like your old charger charges at too high a trickle charge rate/voltage and that is causing the bubbling/venting.

Open circuit voltage is a good indicator of remaining capacity but as you have indicated you need a resting period prior to taking the measurement. Ideally that resting period is long enough for the battery to cool off after heavy use and the voltage to stabilize. Since this is a "rough estimate" you can come close by simply waiting an hour or so and take the voltage measurement then.

If you use a charger specifically designed to charge AGM batteries, you can plug in after every use and won't have to worry about the 50% level. These batteries like to be at full charge and there is no problem with frequent recharging, as long as you don't exceed the maximum trickle charging voltage. Some of these chargers will actually shut the charge completly off when the battery is fully charge and then turn it back on if the battery voltage falls below a certain level.

Your datasheet is indicating that the maximum charge voltage is 14.5 - 14.9 volts and the maximum trickle charge voltage is 13.6 - 13.8 volts.

Tom

Good information guys. Thank you for the input.

I didn't know that hydrogen was odorless. This smell is probably not sulfur because it doesn't smell like rotten eggs. It does have an acrid smell to it so it probably is some hydrogen compound. We've watched videos where people purposely overcharge their SLA. Our batteries are not whistling and there is no visible venting like the videos but they are quite hot to the touch as is the charger brick.

Tom indicated that the maximum charge voltage is 14.5-14.9 V according to the datasheet figures I supplied. The stock charger's output is 24V and 2A. Could this be the reason it is overcharging the batteries? Should we use one with an outputs no more than 14.9V? I hate to waste a charger that is proper and still working but if it's either not the correct voltage or it's cooking the batteries then it needs to be replaced.

I would prefer to buy something other than a uni-task wheelchair charger so we've been looking at chargers such as the Turnigy. The problem with this though is that we're unable to find an XLR (the wheelchair's receptacle) connector adapter that would allow us to use one of the Turnigy cables. We're still looking into that. The alternative is that we refit the batteries with an Anderson connector but my wife isn't too keen on that idea.

Hello ACruceSalus,

If you have 2 batteries hooked up on series you can end up with 24 volts. In that case the maximum voltage would be 2 X 14.9 = 29.8 volts.

If the batteries are hooked in parallel you have 12 volts and charging them with a 24 volt charger will ruin them.

Tom

Hi Tom,

It sounds like I'm using the correct charger then because the batteries are equivalent to the ones that came with the wheelchair. Do you know of anyway to test the charger and do you have any thoughts about using the Turnigy as a replacement?

Hello ACruceSalus,

You can monitor the voltage at the end of the charge. If the maximum voltage exceeds the allowable, you have problems. After the charge is complete you can then monitor the trickle charge voltage and if that exceeds the allowable you once again have problems.

I use the BatteryMinder for my 12 volt charging. I see they have a 24 volt charger as well. You don't want the one for aviation. The BatteryTender also does a good job. Turnigy has a variety of models to choose from, which one were you looking at?

Tom

Tom,

I'll have a look at the battery minder. I ran across it but did not research it. I was considering the Turnigy Accucel-8. If I buy it I was thinking of bypassing the XLR connector by connecting the charger directly to each battery and charging them one at a time. Would this cause balancing problems?

You said I could monitor the voltage at the end of the charge but how do I know when this occurs? I suppose I could take periodic readings over the time that it charges but it is getting too hot before it finishes charging. Unless I misunderstood the maximum charge is 14.9 V for each battery.

Tonight I closely monitored the battery temp by hand every 30 minutes. It was cool until sometime between 1.5 and 2 hours when they were warm to the touch and the brick was hot. I removed them at the 2 hour mark. They went from precharged 13.04V to charged 13.70V and precharged 13.05V to charged 13.71V. I let them rest for an hour and the readings were 13.43 and 13.46.

Now that the batteries have cooled and I've taken the resting voltage I'm going to charge them again and monitor the charging voltage at each battery's terminal.

Tom thank you so much for all this help.

ACruceSalus said:

Tonight I closely monitored the battery temp by hand every 30 minutes. It was cool until sometime between 1.5 and 2 hours when they were warm to the touch and the brick was hot. I removed them at the 2 hour mark. They went from precharged 13.04V to charged 13.70V and precharged 13.05V to charged 13.71V. I let them rest for an hour and the readings were 13.43 and 13.46.

Click to expand...

A resting voltage (taken after a couple of hours) of 13v is likely near full charge. Your 13.43-13.46 readings sound a little high, based on what I typically get after charging SLA AGM batteries. I think your charger is over-charging.

Hello ACruceSalus,

Interesting...

It sounds like your charger is charging at its maximum rate in an effort to get the voltage over 14 volts. At the end of the charge process the batteries can warm up and that seems to be what is happening. It will be interesting to see how the next round goes.

It also sounds like you still have some surface charge after an hour of resting. One of the "tricks" we used to use is to apply a load for a short time after charging to bleed this surface charge off. With a car we would turn the headlights on for a minute or so and then shut them off and take the voltage measurement 15 minutes later. Is there a way you can run the device or if it has a light turn it on in an effort to eliminate this surface charge?

The Accucel - 8 is a reasonable charger. The main issue is that it is programed for flooded lead acid and will undercharge AGM.

Tom

Tom,

I'm glad you told me about how the Turnigy is programmed for flooded cells and will undercharge an AGM. I probably wouldn't have discovered that until after getting it. Do you know of any other charger that is programmed for AGM but also charges NiMH and Li-Ion?

After charging it last night and again tonight I suspect that there is a short in the charger and it's charging at too high a voltage.

The battery datasheet states that the allowable charge voltage range is 2.40-2.50 per cell. So when it charges over 15.00 V then it is not within the allowable range.

After my previous post I put the batteries back on the charger. I initially checked the charging voltage and it was rising but didn't see the starting voltage. At 15 minutes it had risen to 15.26V and 15.34 V. At 40 minutes the charger light was green and the charge voltage dropped back below 14 V but I didn't record the value. The batteries were not hot but the charger was. When I picked up the charger brick and set it back down it switch from green to yellow and the voltage started rising. The charge voltages were still rising at 16.81V and 16.85V when I stopped charging the batteries. That completed the cycle.

After my wife used it I started another charging cycle and the batteries were 13.05 V and 13.06 V. The first column is charge time in hours and fractions of an hour (.25 would 15 minutes, .50 is 30 minutes, etc.).

1.00, 15.42 V, 15.6x V, charger warm, batteries not warm
1.75, 14.99 V, 15.42 V, charger hot, batteries warm
2.00, 14.91 V, 15.37 V, charger hot, batteries a little warmer but not hot
2.25, 14.83 V, 15.44 V, charger hot, batteries a little warmer but not hot
2.50, 14.79 V, 15.38 V, charger a little hotter, batteries a little warmer but not hot
2.75, 14.79 V, 15.33 V, charger was a little hotter, batteries were a little warmer but not hot
3.00, 14.94 V, 15.85 V, charger was hotter and uncomfortable to touch, batteries somewhat uncomfortable to touch, I heard faint bubbling but no smell or venting. they were removed from the charger even though the charger LED was not green.

Rested it for 5 minutes, rode it for 1 minute and they were 13.43 V, 13.45 V. Another 15 minutes rest they were 13.42 V and 13.44 V.

There wasn't an acrid smell and I didn't hear any bubbling until the 3 hour mark.

I let the charger and batteries cool for an 1 hour after removing them from the charger and the voltage dropped to 13.40 and 13.41 before I reconnected them to the charger. I took constant readings on one of the batteries and it steadly rose to 15.65 V at the 10 minutes mark and stayed there for about 1 minute and started dropping to 15.60 where it stayed for about 1 minute and then started raising again.

.25, 15.16 V, 15.69 V
.50, 15.22 V, 15.93 V
.75, 15.31 V, 15.91 V
1.0, 15.79 V, 15.88 V

I removed the batteries from the charger at the 1 hour mark. The charger was hot, the batteries were warm, I could hear bubbling, and there was a faint acrid smell. The charger LED was not green. I rested it for 5 minutes, rode it for 2 minutes and the readings were 13.36 V and 13.38 V. Another half hour rest made .01 drop difference.

Sorry if this is a little long winded but I thought it better to give too much information rather than not enough.

Hello ACruceSalus,

Hobby chargers focus more on nickel and lithium chemistries. They throw in a flooded lead acid algorithm for "bragging rights." I am not aware of any hobby chargers that have expanded their lead acid algorithms to include flooded, AGM, and gell batteries. They may exist, but I am not aware of them.

With that said it comes down to life expectancy. The simple flooded lead acid algorithm will work reasonably well with AGM and the life cycle of your batteries may be more dependent on the depth of discharge than having a little less than a full charge. The problem comes when one cell starts to under perform. Then the battery will get out of balance and fail. A work around for that is to trickle charge for something like 24 hours periodically.

On the other hand spending around 150 for a charger that is designed to specifically charge AGM batteries may pay for itself in extended life of the batteries and peace of mind...

Your testing reveals that you are overcharging your batteries. You need a new charger.

Tom

Tom,

My wife and I have come to the same conclusion as you. We'll have to decide which way to go. Again thank you for your guidance.

WalkIntoTheLight, thank you for your input.

This is a typical indication that the batteries were not balanced *individually* before placing them into service together. Charge each one individually on an external agm charger such as the battery-minder (my preference also) or a battery tender and let them finish their job and rest in float for at least 12 hours. THEN put them into service.

Even if you buy batteries from the same stock, same date, etc, there is no guarantee that each has seen similar storage environments in retail prior to purchase.

If you really want to get into the thick of it, an excellent site dealing specifically with wheelchairs and charging:
http://www.wheelchairdriver.com/
and
http://www.wheelchairdriver.com/board/

Heh, first we'll get you into Odyssey agm's. Then we move you into Lifepo4!