6volt batteries down to 80%....

dlochner · Jun 22, 2019

Do you mean discharge to a 20% SOC?

My understanding is that it is the number of cycles that matter most and long periods of deep PSOC are bad for FLA Batteries. I doubt that discharging to 20% SOC a few times in a batteries life will have a huge difference in the life span, however as a regular practice it would be bad for an FLA battery. If I recall correctly some batteries can go that deep, Lithium batteries and some AGMs, but not the traditional FLA batteries.

Every battery manufacturer has a different charging routine. If you contact them they will/should give you that information. Have you looked at this post: https://marinehowto.com/programming-a-balmar-voltage-regulator/

Don S/V ILLusion · Jun 22, 2019

I know someone once posted a chart as I recall by some battery manufacturer showing cycles vs. depth of discharge numbers. It might be in the archives searchable here or discoverable via an internet search. Can’t recall the substance of that data.

Stu Jackson · Jun 22, 2019

NYsail, I've shamelessly copied this from the parallel discussion on marine sanitation from Peggy [I sense her frustration]:

you've been on sbo.com for nearly X years... You've posted nearly 400 times on other topics, read a lot of my posts, even liked a few. ..........................

Have you been unaware of basic battery issues? Have you not been reading the material that Maine Sail posts about batteries and their care & feeding?

Running FLA batteries below 50% severely decreases their life cycles.

But, this has been going on for the last 50 years with batteries in boats.

Nothin' new here.

80%?

I disagree.

And before I get flamed, maybe I'm misinterpreting your question. Which was:

NYSail said:
I have been told that instead of discharging batteries to 50% you can discharge to 80%......... is that true In real life usage?

That's simply very questionable. Perhaps for new tech batteries, but for recreational boats with "usual" battery technology? Nope.

Sorry, but it's true.

Beware of the "I have been told..." part. By whom?

Don S/V ILLusion · Jun 23, 2019

Stu Jackson said:
Have you not been reading the material that Maine Sail posts about batteries and their care & feeding?

Beware of the "I have been told..." part. By whom?

I think that’s the problem - just because someone claims that doesn’t make it true nor does it apply universally. The “I have been told” part applies to everyone.

Count me among the list of people who prefer to know. Throughout the years/decades we have had boats, I never bothered much worrying about battery SOC and the lifetime of our batteries never suffered measurably. I too wonder how ‘big a deal’ it is.

dlochner · Jun 23, 2019

Don S/V ILLusion said:
Count me among the list of people who prefer to know. Throughout the years/decades we have had boats, I never bothered much worrying about battery SOC and the lifetime of our batteries never suffered measurably. I too wonder how ‘big a deal’ it is.

An epistemological question!

How do we know what we know? Don, playing the Devil's advocate here, how do you know your batteries "never suffered measurably?" Did you run a controlled experiment? Or are you simply satisfied with the life of your batteries? And by what measurement did you determine that the batteries never suffered measurably?

I'm not trying to be argumentative about battery life, it is just in any endeavor we need to know how one comes to know what they know. And that was sort of Don's point, when he says "The “I have been told” part applies to everyone."

Aura and mystic abounds and surrounds. One of my favorites is the dangers of Acetone. If you are a nitrile glove, acetone is indeed dangerous as it penetrates and weakens nitrile. But if you are a human, it's not healthy, but the dangers are pretty minimal. It is not a known carcinogen nor is it necessarily fatal if ingested. It is not a good thing to ingest, and you'll get sick, but probably not die. You probably don't think much about the dangers of nail polish remover, in which the active ingredient is acetone.

Going back to the original question, can you discharge a FLA battery to 20% SOC? Yes you can. But it will take its toll and measured in terms of chronological life span, it will shorten its life. In terms of the number of charge/discharge cycles, I am not as certain. Each discharge/recharge to 50% SOC is .5 cycles, each discharge/recharge to 20% SOC is .8 cycles. Thus, over a five day period, discharging to 20% and recharging yields 4 cycles. Doing the same to 50%, is only 2.5 cycles.

The whole battery dying process is more complicated than I'm presenting because of sulfating and age, however, looking at just one dimension, discharge/charge cycles it is easy to see that shallower discharges will lead to a longer life measured in months and years, the way most of us consider battery life as the number of years a battery lasts.

And don't forget, the battery salesman wants to sell you batteries, the faster you need to replace them the better the battery sales will be.

dlochner · Jun 23, 2019

NYSail said:
And when I questioned the 80% specifically the gentleman from Trojan said periodically discharging to this level is ok

This begs the question, what is periodically? Once a season? Once a week? You'll probably never get an answer from Trojan on that question.

"So, what's periodically mean?"
"Oh, once in while."
"How long is a while?"
"A little bit."

Don S/V ILLusion · Jun 23, 2019

dlochner said:
This begs the question, what is periodically? Once a season? Once a week? You'll probably never get an answer from Trojan on that question.

"So, what's periodically mean?"
"Oh, once in while."
"How long is a while?"
"A little bit."

To state the obvious, nobody knows since you can't measure either "a while" or "periodically".

And since we can't know definitively how long batteries last under all conditions, we similarly can't know if or how many cycles they last longer under one condition.

Having said that, I can measure "a little bit" - that's when i try to eyeball which socket will fit a bolt head and I'm always off a little bit.

Davidasailor26 · Jun 23, 2019

NYSail said:
I’ve always heard never......

Well, Maine Sail's capacity test procedure brings the battery to 0%, and he says that's ok to do annually, so it's not a binary thing that once you hit 49% you're done. What I'd be looking for is more quantified data from Trojan to back up that guy's claim. If the competitor's battery does 1000 cycles to 50% but 500 cycles to 80%, does the Trojan do 501 cycles to 80%? 999 cycles? Somewhere in between? That's really the question you need to see the answer to.

Mark Maulden · Jun 23, 2019

I buy my batts right off the line at Dyno in Seattle. They provide a lot batts for the PNW fishing fleet. I’ve asked them a few of these questions along with peukert factors etc. Maine says they are way behind the curve in this area. Then again, do you really care if your batts fail at 7 yrs vs 7yrs 6 mo? (Figuratively speaking). Are you going to be the engineer that keeps track of all this or are you just going to go sailing and use your boat? I know what I do...

Stu Jackson · Jun 23, 2019

NYSail said:
Sorry my question frustrated you so much.....

Well i am a very novice guy when I comes to designing electrical systems and also I am very curious in learning as I enjoy doing most work myself...... I’m not just a guy that buys and moves on..... I like to understand.

NYS, I completely agree.

I don't know if you've seen this, although IIRC you said you've read MS's website info.

https://marinehowto.com/what-is-a-deep-cycle-battery/

Touches on some of the issues.

I'm sure there actually charts from different vendors available as Don said. If I run into one, I'll let you know.