Funky behavior from Sealed Lead Acid (SLA) 12 volt batteries

[darcyh]

I keep a few SLA batteries around for UPS units. They were all purchased new and are stored at room temperature. Various brands all made in China. Age of the batteries is 3 months to four years. Sizes are 18ah, 14ah and 7ah. Every three months I top up the charge. They have never been heavily discharged, dropped or any physical damage.

Here is what I am running in to. Read standing voltage 12.7 volts with a Fluke 87V meter, then connect a 'load' a two amp light bulb. No or very low output from bulb. Then over a few minutes the bulb will increase in brightness to full brilliance. The meter is now reading 12 volts. While this bulb is on, I connect a second bulb; and the volts drop again. Over a few minutes voltage ramps back up to around 12 volts and the bulbs go bright.

I have a gizmo that tracks the amount of current (AH) extracted from the battery. I can take 3 or 4 amp hours out of the battery and recharge it. It will take a full recharge. For a few days the behavior will cease and the light bulbs illuminate at full brilliance upon connection.

Wait 10 days or so and the cycle repeats. I just experienced this with a two year old battery. Once this happens the battery is unreliable and I discard it. It's almost like there is an initial resistance that must be overcome before the battery will discharge. I've had this happen with two 18ah and one 7ah battery.

Has anyone else experienced this? Can you explain what is going on? Is there a way to prevent it?

Thanks for any explanation.

 

[turbodog]

Do the batteries sit for 3 months disconnected from all devices? Or are they being float charged by the ups units?

 

[darcyh]

Should have been more clear, these batteries are completely disconnected and have had no load applied to them for the past few months.

Regards

Dave

 

[turbodog]

Maybe a bad charger... could be damaging the battery somehow. Or charger not designed for SLA?

If you can put this charger on them... could be worth a try (outside of course). I've had very good results with the 'repair' mode on it with some flooded car batteries. It does have an AGM setting.

The rising voltage sounds like an issue w/ the plates... some sort of coating not allowing electrolyte to reach reactive material.

SLA is supposed to work in any orientation... try turning on the side just for kicks.

Dissect a dead one. See what the electrolyte levels are. See if the plates are warped. Etc. (wear goggles, face shield, have fresh water handy, be careful).

 

[darcyh]

I usually use a Battery Tender 1.2 ah charger or the pb function on a Junzi i-charger. I will try using a Noco in desulfator mode. Perhaps this may help. I'll also try flipping it over. Thanks for the suggestions.

Dave