Sla/agm battery charge anomaly

[stormtracker78]

Hi I have a question for those experts out there concerning charging your AGM or SLA battery I have 2 mighty Max 12 volt 15 amp hour batteries I charge them with a 4 amp suoki battery charger I use the SLA setting as I believe thats what the batteries are but I've been told SLA and agms pretty much are the same configuration when it comes to charging that's my first question my second is when I charge them to full within an hour after I'm done charging they drop down from full to 12.66 percent they're both pretty dependable on staying that charge but I've hardly ever used them and I never went below 50% when I did use them and at 12.66 volts under the soc guide is 80% charge should they drop from 100% charge to 80% within an hour and remain there in storage? that's my anomaly I can't seem to find anything any info would be greatly appreciated

 

[sunshine_eggo]

SLA are typically flooded lead acid batteries that are sealed with valves designed to retain some pressure and limit the electrolyte losses.
AGM are Absorbent Glass Mat with the electrolyte saturating the mat. They have less electrolyte and typically have different alloying elements and operate at a slightly higher voltage.

All lead acid batteries must be charged to something in the 13.8-15.0V range (lots of variables in that range) in order to be fully charged.

Once charge is removed, voltage naturally settles. Again, lots of variables, but 24 hours is a typical rest period (no charge or discharge of any kind) where the voltage correlates to a state of charge.

Voltage-based SoC in an active system (charges or discharges) is completely and utterly useless.

Only a battery monitor that actually counts the amps in and out of the battery and then compares the net to the programmed battery capacity can give an accurate state of charge, e.g., the battery monitor counts an average of 10A for the last hour on a 100ah battery. (100Ah - 10Ah) / 100Ah = 90%.

 

[stormtracker78]

SLA are typically flooded lead acid batteries that are sealed with valves designed to retain some pressure and limit the electrolyte losses.
AGM are Absorbent Glass Mat with the electrolyte saturating the mat. They have less electrolyte and typically have different alloying elements and operate at a slightly higher voltage.

All lead acid batteries must be charged to something in the 13.8-15.0V range (lots of variables in that range) in order to be fully charged.

Once charge is removed, voltage naturally settles. Again, lots of variables, but 24 hours is a typical rest period (no charge or discharge of any kind) where the voltage correlates to a state of charge.

Voltage-based SoC in an active system (charges or discharges) is completely and utterly useless.

Only a battery monitor that actually counts the amps in and out of the battery and then compares the net to the programmed battery capacity can give an accurate state of charge, e.g., the battery monitor counts an average of 10A for the last hour on a 100ah battery. (100Ah - 10Ah) / 100Ah = 90%.

Ok ty attaching a picture of my battery so basically all I'm doing is charging my battery up with a battery charger that is a smart battery charger it shows the amps in and out and the voltage when it says full the battery is at 13.8%. after 1 hour after it's done charging and I have removed the charger it's back down to 12.66% which from what the chart shows means 80% as regards to an active system I don't have one I just charge my batteries every 3 months to keep them in good shape but like I said I just can't figure out why after I charge them full they drop down within an hour I would figure yeah every 3 months they would get down to that but one hour that's what's throwing me off some of the stuff you said I need to research as I'm not in depth as what you said but it's great knowledge and gives me something to research to find out why thank you

 

[sunshine_eggo]

By 13.8% and 12.66%, I assume "%" should be "V"?

Your picture is blurry. I can't read the smaller text where I expect cyclic and standby voltages are given.

13.8V is not adequate to fully charge a battery unless it is held there for a significant time - 24 hours is typically sufficient.

 

[stormtracker78]

By 13.8% and 12.66%, I assume "%" should be "V"?

Your picture is blurry. I can't read the smaller text where I expect cyclic and standby voltages are given.

13.8V is not adequate to fully charge a battery unless it is held there for a significant time - 24 hours is typically sufficient.

Remember I said that it's charged with a smart charger that being said it's charged at 14.8 volts after it's full it'll be at 13.8% standard use or standalone the charger will say full at 13.8 so then I disconnected so I know it's being charged correctly all I am trying to find out is why a battery will drop from full charge and lose 20% after it is properly fully charged when you remove the charger within an hour if your monitoring it with a volt ohm meter to check it while it's being checked you can see the voltage dropping little by little to it finally levels off at the 12.66 and stays there I'm just trying to find out if that means one of the cells is bad inside the battery here is a clear picture also
yes the percentage should have been volts sign my Android is not the best or my brain?

 

[sunshine_eggo]

Again, your conception that the 80% or 100% or anything being reported to you in % is accurate. It is not. It is a completely worthless value unless you know how it's getting that value. It has no idea how big the battery is, and it has no idea if any charge has been lost or consumed, thus it is literally impossible to accurately know the state of charge.

What is your battery voltage 24 hours after disconnecting the charger?

If it's > 12.6V, it's 100%.

If your goal is to protect these batteries while in storage, hold them at the float voltage/standby use voltage (13.6V preffered).

 

[stormtracker78]

Again, your conception that the 80% or 100% or anything being reported to you in % is accurate. It is not. It is a completely worthless value unless you know how it's getting that value. It has no idea how big the battery is, and it has no idea if any charge has been lost or consumed, thus it is literally impossible to accurately know the state of charge.

What is your battery voltage 24 hours after disconnecting the charger?

If it's > 12.6V, it's 100%.

If your goal is to protect these batteries while in storage, hold them at the float voltage/standby use voltage (13.6V preffered).

Okay well I do want to protect them while in storage how do I hold them at the float voltage standby voltage? Would that mean I leave them hooked up to the battery charger constant? Also when I say percent I mean volts which I've already stated when my volt/ohm meter says 12.66 volts I looked that up on the AGM chart which says 80%. That's where I was getting that from but then there's another chart that says 90 I remember hearing in the form that those charts are very seldom accurate though also in an emergency situation when you're using them you've got to go by your volts to know when you're at 50% to not drain them down and recharge them accurately so you've got to have some kind of percentage based off the volts so if you're saying 12.6 is 100% full charge what would be the voltage for 50% charge? Is this chart accurate?

 

[sunshine_eggo]

Those charts are approximations.

If these are for backup purposes, you should keep them on the charger if the charger holds them at 13.8V to ensure they are fully charged and ready to go when needed.

 

[stormtracker78]

Those charts are approximations.

If these are for backup purposes, you should keep them on the charger if the charger holds them at 13.8V to ensure they are fully charged and ready to go when needed.

Awesome ty my charger does hold at that voltage when it is done my charger is a smart suoki 4 amp charger from Amazon quick question is a battery charger and battery maintainer the same thing would a maintainer be better if it's not a charger for keeping them charged for backup? I really appreciate all your advice and knowledge thank you again the reason I asked is I wanted to put several batteries in parallel keeping them fully charged until I need them I read somewhere that battery maintainers are good for this process but if my charger is the same as a maintainer well then I might as well just use that I can send a pic if you need it

 

[sunshine_eggo]

It's hard to say what the marketers mean by their terms. I have owned many devices with both labels that failed to deliver on one

There are three stages to properly charging a SLA/AGM battery:

1) bulk charge (stage 1) = send maximum amps to the battery while below the absorption voltage.
2) absorption charge (stage 2)= hold battery at maximum voltage and allow current to taper until it drops to 2% of capacity (.02 * 15Ah = 0.3A) where it is fullycharged.
3) float (stage 3)= holding the battery at an elevated voltage to ensure the battery is held at 100% charge and does not degrade. This may be done indefinitely. Batteries designed for standby applications may last up to 10 years simply being held at 100% ready for backup use.



In your case, the absorption voltage is identified by the cyclic use voltages. The float voltage is identified by the standby use voltage.