My FLA battery has a resting, charged voltage of 12.85V (2.14 V per cell). A problem?

[Vigilant24]

My new 12V flooded lead acid marine "deep cycle" (I know....) batteries are both showing a higher than expected fully recharged resting voltage of 12.85. I'm pretty sure this isn't just surface charge because it's been days since I charged them and I've also loaded them at 40watts for a several minutes immediately after charging. I don't think it's a reading error: both my VOMs and the inverter agree on the voltage. This is at about 65F (18 C), which makes things stranger still.

In general, the documentation for FLA batteries indicate they should be at about 12.7V (2.1V per cell)

My specific gravity readings are also higher than I'd expected.

I believe the batteries are made by Exide for the marine market. Should I be concerned about the somewhat higher than standard voltage when fully charged? Are there differences in battery chemistry (amount of antimony, etc) that could explain this discrepancy?

Thanks for any assistance.
Mark

 

[sunshine_eggo]

Voltage is analogous to SG. If your SG are higher than spec, that explains it. Worth checking that your fluid levels are correct.

There are variations in plate composition that can alter resting voltage and also affect self-discharge rate. If your plates include Calcium more common to AGM, they may run a little higher and self-discharge a little less.

 

[Vigilant24]

Voltage is analogous to SG. If your SG are higher than spec, that explains it. Worth checking that your fluid levels are correct.

Thanks. The fluid levels look okay (at least no plates exposed and no cells overfilled). Well, I'll just assume there's something about the chemistry that accounts for this and maybe I'll just adjust the other voltage = % SOC points to account for it. An additional 0.15V at the sum of 6 cells only corresponds to a 10% difference in SOC over most of the usable range. It's not like this is a very precise business anyway.

After I get a coulomb counter and run a few tests I can build my own chart for "% SOC = XX SG and/or XX resting voltage."

Thanks again.
Mark

 

[yodamota]

any chance you could tell us how the batteries are being charged?

 

[Vigilant24]

any chance you could tell us how the batteries are being charged?

I used a vintage 1990 "smart charger" (Schauer model CR312, 10A max). They've scarcely been used or charged. I bought them in early March and their date of production was Jan 2022. As received, they were at 12.69V (62degF). I'm virtually certain they received no charging while on the shelf at Rural King, so I suspected this high voltage after 3 months of sitting was due to an inaccurate voltmeter or something else. So I gave them a brief time on the charger (14V, automatically rapidly decreased from 5A at start to 2A, I left it on for 90 minutes). I let them rest 24 hours and measured 12.8V and a specific gravity of about 1.30. Tis staryed the same after applying a 40w load for a few minutes each. I then used 1 battery to run an approx 20W load for 9 hours, (so, should have been about 15 AH withdrawn from that 115 AH battery) and the battery voltage was at 12.71, corrected specific gravity measured approx 1.25. So, the battery >should< have been about 10% discharged, but my voltage reading was consistent with a fully charged normal FLA battery and my specific gravity was consistent with an approx 95% SOC.
I suppose the higher resting voltage of these batteries is not a big deal in itself. I suspect it is due to their chemistry. The only significant inconvenience is that, apparently, I may not be able to rely on my NOCO or other smart charger to keep them at >their< 100% SOC. If a 90% SOC on >these< batteries is really 12.7V but the charger sees that as "full", it may not actually do anything to top them off until they've self-discharged even farther.

Mark

 

[Vigilant24]

I suppose the higher resting voltage of these batteries is not a big deal in itself. I suspect it is due to their chemistry. The only significant inconvenience is that, apparently, I may not be able to rely on my NOCO or other smart charger to keep them at >their< 100% SOC. If a 90% SOC on >these< batteries is really 12.7V but the charger sees that as "full", it may not actually do anything to top them off until they've self-discharged even farther.

Mark

Thinking more on this--I could buy a small resistor between the battery and the terminal clamp to the NOCO so that the NOCO "sees" a battery voltage that is about 0.1V lower than the actual voltage. That would induce the charger to come on earlier and stay on until the battery has reached a voltage of about 12.8 V (which the NOCO would "see" as 12.7V).
But--the charger doesn't have a "sense" wire, it just uses the same cable it uses to charge with. So, the charge (up to 5 A) would be running through that resistor when the charger came on.

 

[sunshine_eggo]

Thinking more on this--I could buy a small resistor between the battery and the terminal clamp to the NOCO so that the NOCO "sees" a battery voltage that is about 0.1V lower than the actual voltage. That would induce the charger to come on earlier and stay on until the battery has reached a voltage of about 12.8 V (which the NOCO would "see" as 12.7V).
But--the charger doesn't have a "sense" wire, it just uses the same cable it uses to charge with. So, the charge (up to 5 A) would be running through that resistor when the charger came on.

Resistors only work when current is flowing. As less and less current flows, the voltage disparity approaches zero. The only thing the resistor would do is decrease current sooner and make the charge take longer, but it would end at the same voltage.

I'm not at all concerned with the charger. 14.0V is actually pretty conservative.

I can't see that you have a problem either with your batteries or your charger. Charge them in accordance with the manufacturer's recommendations (or at least as close as you can), and you're good.

 

[Tunafish]

I ran across this because i have the same situation... I am guessing the batteries where Everstart Max 29DC? That is what i have and have the high resting SOC. They do say maintenance free so calcium seems like the right answer. Anyone know a good float voltage target for these? I am coming up empty in my searches.

 

[Thohean]

Pretty much all of the lead acid batteries I've ever used, when fully charged, came to 12.8 volts. Starting, marine, tiny lawn mower batteries; even the ones from computer UPS read 12.8v. I've switched everything to Lithium, so I can't double check my memory, though.

 

[sunshine_eggo]

I ran across this because i have the same situation... I am guessing the batteries where Everstart Max 29DC? That is what i have and have the high resting SOC. They do say maintenance free so calcium seems like the right answer. Anyone know a good float voltage target for these? I am coming up empty in my searches.

13.5V