Found this while poking around. https://forums.sailboatowners.com/index.php?threads/specific-gravity-vs-actual-ah-capacity.185414/
State of charge, from MaineSail.
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Uhh, thanks, I think. I gather Mainsail is our version of SternWake...
The article was confusing to me but that doesn't take much...
Most all I could get out of it was that the author doesn't accept cell specific gravity readings as proof of state of charge, if cells vary by .50 then then a cell is bad, and using a hydrometer can contaminate cells.
I did not realize that the standard (from someone) for batteries (FLA) being considered "good" for loads is 80% of their rated amp hour capacity. I'd have thought lower, but then, I'm just showing my ignorance.
For someone really into testing battery s.o.c. Then this is great reading and probably somewhat controversial.
The article was confusing to me but that doesn't take much...
Most all I could get out of it was that the author doesn't accept cell specific gravity readings as proof of state of charge, if cells vary by .50 then then a cell is bad, and using a hydrometer can contaminate cells. I did not realize that the standard (from someone) for batteries (FLA) being considered "good" for loads is 80% of their rated amp hour capacity. I'd have thought lower, but then, I'm just showing my ignorance.
For someone really into testing battery s.o.c. Then this is great reading and probably somewhat controversial.
SternWake
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Mainesail has forgotten more than I know.
After a LA battery only has 80% of its capacity remaining, the potential for a cell shorting out increases greatly.
Not that it is easy to figure out just when a battery crosses that threshold.
An Acurate test of a 100Ah battery is if it can privide exactly 5 amps for exactly 20 hours before voltage hits 10.5v. As the amps usually change when voltage drops, getting a constant 5 amps for that whole 20 hours is quite difficult without special equipment. Also, the battery is to be held at exactly 77f the entire test.
I am not sure if the 10.5v is the rebound voltage, after the 5 amp load is removed and X amount of time allowed to pass, or while the 5 amp load is still being applied.
In general the true 20 hour capacity test, is the only way to accurately know the remaining capacity and health, but it is also very abusive to the battery being tested.
With all the unknown and the difficulty of quantifying battery health, I recommend people just get them to as high a state of charge as possible whenever possible, and then there should be no surprises when they are worn out several years later, unless achieving full charge is a total pipe dream with their charging sources. "But But I drove for 15 minutes..........."
Only the cluelessly ignorant should be surprised by premature failure. Problem is they blame all the components other than the selfie taking overdepleting undercharger in the mirror.
After a LA battery only has 80% of its capacity remaining, the potential for a cell shorting out increases greatly.
Not that it is easy to figure out just when a battery crosses that threshold.
An Acurate test of a 100Ah battery is if it can privide exactly 5 amps for exactly 20 hours before voltage hits 10.5v. As the amps usually change when voltage drops, getting a constant 5 amps for that whole 20 hours is quite difficult without special equipment. Also, the battery is to be held at exactly 77f the entire test.
I am not sure if the 10.5v is the rebound voltage, after the 5 amp load is removed and X amount of time allowed to pass, or while the 5 amp load is still being applied.
In general the true 20 hour capacity test, is the only way to accurately know the remaining capacity and health, but it is also very abusive to the battery being tested.
With all the unknown and the difficulty of quantifying battery health, I recommend people just get them to as high a state of charge as possible whenever possible, and then there should be no surprises when they are worn out several years later, unless achieving full charge is a total pipe dream with their charging sources. "But But I drove for 15 minutes..........."
Only the cluelessly ignorant should be surprised by premature failure. Problem is they blame all the components other than the selfie taking overdepleting undercharger in the mirror.
The decline accelerates quickly once below 75-80%, and they're less efficient accepting charge then as well.This world isn said:
And can fail catastrophically too, the longer you keep them around after that point the more likely to cause collateral damage to property or people.
Recording benchmarks when the bank is new is a good idea, something to compare to every quarter or six months.
SmartGauge is the only battery monitor that dynamically adapts its % SoC readings to account for the inevitable walkdown in capacity.
With shunt-based coulomb-counting units, you need to periodically recalibrate them to the new AH capacity, and the 20-hour test required to do so accurately is pretty tedious.
When people report 10+ years still going strong from their top-quality lead bank, it's usually not the result of just spending the money, but going to this sort of trouble, learning how to never be surprised.
Obviously being out in the middle of the ocean is a strong motivation
