0.5% X 20C for 100% SOC - myth?

[conachair]

Originally Posted by john61ct

No, fully charged, or 100% SoC, is when you've met the maker's definition, and are not causing harm to the battery.

How do you know this?

Would be interesting to see any real data, the life of a lead acid battery on a boat must be a small market and quite different to the lives of most, the manufacturers presumably need to come up with a 'catch all' datasheet trying to have the least recalls over all the situations the batts are in, not necessarily the best for a boat.
Though doubt very much there will be data on only ever charging to the documented end current against fully charging. Would need an awful lot of time and money to test different sets of batts but if you have data it would be interesting. Only thing close I've come across was the fabled sandia paper not available on the web which recommended much higher absorption voltages for minimum 3 hours -
L-16 recommended charging voltages - OutBack Power Technologies User Forum

[john61ct]

The definition of terms, and what the ideal proper care specs are, do not vary by the context.

What an owner can achieve in **meeting** those specs of course does, but that's not what we're talking about.

Again, "the documented end current" is the exact definition of" fully charging".

You talking about charging until **absolutely zero further charging is possible**, is just not a thing, other than "overcharging",

in practice pointless and in fact harmful to all sealed batteries.

So of course, no one would bother collecting data on doing that, afaik.

With "conditioning" protocols, deep/full cycling to restore capacity, capacity testing, commissioning procedures, equalizing charge i.e. going to higher voltages etc etc are all spec'd out as terminating **long** before what you're talking about.

But three hours is certainly not a long Absorb / CV stage in that context, especially using higher Bulk / CC currents, out of a 7+ hour charge cycle an AGM bank might hit CV not long after an hour, much much earlier and at a lower SoC% than at a low current.

https://marinehowto.com/how-fast-can...ry-be-charged/

[conachair]

Originally Posted by john61ct

You talking about charging until **absolutely zero further charging is possible**, is just not a thing, other than "overcharging",

Not really, I'm talking about blindly relying on manufacturer's datasheets which might well be a good catchall for them for all the varying uses their batteries have but which may or may not be the best thing to do on a boat. And asking if you had any data to show that following their tail current instead of going further leads to greater battery lifespan. Is your definition of 'overcharging' , which actually defines fully charged when the battery current stops getting any lower , any data to show that it's worse for a battery to do this than to stop at some arbitrary point before this?
So any data at all would be of great interest, I suspect for a great many sailing boats getting to 100% is a rare occurrence, getting all the way back up when you can could very well be a 'good thing' .

But no data to show this, as you've no data to show otherwise....

[john61ct]

Originally Posted by conachair

which actually defines fully charged when the battery current stops getting any lower

Now you are changing horses mid stream.

The above is indeed the definition of Full by many makers.

What I understood from above, was you were saying it's OK to charge until current accepted is **zero amps**.

Which it is not, and is also of course completely different from your quote above.

[Bycrick]

The manufacturers make recommendations not dicta. Those recommendations are based on things like science, legal liability, expected use cases, ease/cost of manufacturing and perhaps whether the engineer had toast for breakfast. They’re unlikely to be willing to tell you why they picked the numbers that they did.

Notice that the language used in the snippets from at least one manufacturer is "that the battery MAY BE CONSIDERED fully charged." That allows a considerable amount of wiggle room.

I find the idea of "overcharging" a flooded LA battery on most live-aboard sailboats to be ludicrous. With about 800AHs of L-16 batteries, I have a big alternator compared to most people I’ve seen and it’s barely capable of 0.2C. They 2800 watt inverter/charger will do about 0.12C. The almost 500 watt solar array is even less.

So unless I were to leave the batteries unwatered for a long time, there’s essentially no way to "overcharge" the batteries.

The manufacturer's suggestions are based on what they think their average customer will be doing. After that, you need to know what you’re doing to figure out what’s best. Or you can just accept all the defaults and pray a lot.

[john61ct]

Sorry I did not think I needed to ask explicitly, which of those two definitions did you mean?

And yes I agree about FLA, just keep the water up no worries.

I specifically mentioned sealed, and besides AGM, GEL banks are very susceptible to overcharging

Most spec endAmps of .005C but a gentler 0.015C still gets you to 100% SoC.

With Deka's just confirm 12.85V isolated resting.

There simply is no reason to push past that, with all VRLA lines, you just can't restore lost electrolyte levels.

[conachair]

Originally Posted by john61ct

Now you are changing horses mid stream.

The above is indeed the definition of Full by many makers.

What I understood from above, was you were saying it's OK to charge until current accepted is **zero amps**.

Which it is not, and is also of course completely different from your quote above.

No, not zero amps, you'll never get there. That wasn't what was said. Lets try again -

No, fully charged, or 100% SoC, is when you've met the maker's definition, and are not causing harm to the battery.

How do you know charging a boat battery in 'normal' use is getting damaged more by charging until the tail current stops going down (about 0.5% or a bit more for T105's) than by stopping charging at 3%? Other than blindly following a spec sheet.

Answer, none of us know unless someone has a huge pile of testing data. I'm more for keep going past the trojan figure when it's sunny and you can, not every day it's possible to even get that far.

[john61ct]

Originally Posted by conachair

No, not zero amps, you'll never get there. That wasn't what was said.

In which case that's fine, often the official spec

So we're not in any disagreement worth pursuing further,

sorry if I misunderstood