Measure present Full Battery Capacity (as it declines)

[Maine Sail]

Originally Posted by wsmurdoch

Wouldn't a "sulfated" battery have much of its sulfuric acid permanently and irreversibly converted into lead sulfate reducing the amount of sulfuric acid in the electrolyte and lowering the specific gravity of the fully charged "sulfated" battery?

Not always. I routinely test batteries that can deliver a perfect "full charge" 100% specific gravity reading yet can barely muster 20-30% of the rated Ah capacity.

[rgleason]

Originally Posted by wsmurdoch
Wouldn't a "sulfated" battery have much of its sulfuric acid permanently and irreversibly converted into lead sulfate reducing the amount of sulfuric acid in the electrolyte and lowering the specific gravity of the fully charged "sulfated" battery?

Originally Posted by Maine Sail

Not always. I routinely test batteries that can deliver a perfect "full charge" 100% specific gravity reading yet can barely muster 20-30% of the rated Ah capacity.

Zil wrote
Lead acid batteries don't lose capacity (AH) because the acid weakens (SG). Rather they lose capacity because the plates deteriorate. They still can charge to full voltage and high SG. They just will not last as long.

Good question. I asked it awhile ago, but did not see any response. Thank you. So Specific Gravity is not necessarily a good indicator of battery health or capacity!

The darn things are more elusive than the Heisenberg uncertainty principle, no actually the observer effect

I guess the answer for most is a SmartGauge for the next 10 years until some other better device is made.

[hellosailor]

Despite all the folks who swear by desulphators (and sell them) and the many YouTube videos that say all you have to do is dump the old electrolyte and add epsom salts....the battery MAKERS all say that after as little as 30 days of standing without a charge, a wet battery will form SOME permanently insoluble sulfates. And that SOME permanent damage will always occur from them. This is why they also leave space at the bottom of the battery, below the plates, to allow the sulfates to precipitate out and form totally clear below the plates.

There's a big difference between what you can do and can measure, and what might be possible to exactly what extent.

Even JCI has pages on their web site claiming their exclusive new age grid pattern (not just a plain tiled pattern anymore) will promote better plate reformation and better overall battery life. Could just be smokesmanship, but that kind of stuff does matter, and there is some science and a lot of research (and hookum) behind it.

[john61ct]

Originally Posted by rgleason

I guess the answer for most is a SmartGauge

As long as you realize you're just getting the most accurate guesstimate of SoC, not displaying state of health (residual capacity).

Again, 20-hour load test is the only reasonably easy low cost way to get SoH directly.

[wsmurdoch]

Originally Posted by Zil

Lead acid batteries don't lose capacity (AH) because the acid weakens (SG). Rather they lose capacity because the plates deteriorate. They still can charge to full voltage and high SG. They just will not last as long.

Originally Posted by wsmurdoch

Wouldn't a "sulfated" battery have much of its sulfuric acid permanently and irreversibly converted into lead sulfate reducing the amount of sulfuric acid in the electrolyte and lowering the specific gravity of the fully charged "sulfated" battery?

Originally Posted by Maine Sail

Not always. I routinely test batteries that can deliver a perfect "full charge" 100% specific gravity reading yet can barely muster 20-30% of the rated Ah capacity.

I’ve been trying to wrap my head around this.

I know flooded lead acid batteries can fail for many reasons... The active material (lead sponge or lead peroxide) can be shed from the plates and be lost to the bottom of the cells. The lead grids in the positive or negative plates or the connecting bars can corrode away leaving parts of the plates or whole plates without electrical contact with the poles of the battery. There can be an internal short between a positive and a negative plate in one cell that discharges that cell internally either quickly or slowly depending on the resistance of the short reducing the capacity of the whole battery. The fluid level in the cells can fall below the plates leaving them exposed to the air and ruining them. Mechanical shocks can break connections within the battery. I don’t know; there must be still other reasons for FLA battery failure that I have not heard of.

I was writing about one particular failure mode, sulfation, where the plates become covered with a form of lead sulfate (different from the normal lead sulfate) that (unlike the normal lead sulfate) cannot be converted back into lead or lead peroxide by recharging the battery. Where else can the sulfate in the lead sulfate come from except from the sulfuric acid in the battery fluid? If recharging a "sulfated" battery fails to convert the lead sulfate back into lead or lead peroxide, wouldn’t the concentration of sulfuric acid and thus the specific gravity of the battery fluid be reduced from its new-battery-fully-charged value?

I’m puzzled.

Bill

[Zil]

Hey Bill. It is hard to figure. I have seen many batteries test to volts and also SG, yet not have more than a few minutes life. Sounds like you can do a test?

[wsmurdoch]

I have seen batteries with a good high specific gravity in all the cells and a good high battery resting voltage when connected to a load drop quickly to a low battery voltage. I assume that those batteries failed due to one of the other causes that I listed; not sulfation. They would fail a test with a carbon pile battery tester and would not keep a car headlamp burning for long.

[john61ct]

Since standard EoL is 80% SoH

even if pushing to 70-75% is low risk, at least for those cruising close to places with reasonably priced replacement batts,

I would think a properly maintained system would rarely, if ever, need to deal with many of these issues.

No surprises, should be the primary goal.