Battery lifetime/cost vs. state of charge

[Stu Jackson]

Originally Posted by kmacdonald

...........................I don't know how some people cross the street on their own.

So you could clearly explain to them just to do so. Smaller boat, smallest bank, works for you. As I've mentioned many times regarding your very qualified opinions, your situation may not, I say MAY, not, be applicable to folks with larger boats and larger energy budgets. But you have been very good at explaining what your thoughts are and why. Thanks.

[kmacdonald]

And good looking.

[chala]

Originally Posted by Cadence

I think his reef is an absorption unit. If done right the propane is no problem and highly efficient

Originally Posted by atoll

explosion and fire!

Originally Posted by Cadence

That is crass.

You do not really teach old monkeys how to make grimaces.

[chala]

I have four house batteries in three banks plus one starter.
One of them is discharged between 30 to 40 % more than the other 3, just under 12V. After 1 year and more than 300 recharges, all four batteries capacity tests the same if it is for the starter one that shows some diminished capacity.
After 2 years and more than 600 recharges, still the same. The warranty for the batteries is of 18 months so I get new batteries, 22kg each, easy to replace.
I repeated the test for 2 more years and another 2 years, still the same result.
The above is no workshop bench test or manufacturers test but normal cruising test.
Discharging two batteries between 30 to 40 % more than the other could be done but I do not have the need.

[kmacdonald]

What brand of batteries? Do you always recharge to 100 percent.

[sailorboy1]

so many slaves to batteries out there

[kmacdonald]

I think it's safe to say that if you don't recharge to 100% SOC on a routine basis you will not get good service life out of LA batteries regardless of DOD.

[a64pilot]

If you have an unlimited charge source, say a Megawatt Solar array, and 1 100 amp lead acid that is discharged to 50%, it's going to take a min of five hours to fully recharge it, add a little age to that battery and it takes longer, the further you discharge it, the more time you add to fully recharge.
Yes I know many who say their bank is fully recharged by noon, you know the little green light comes on and their battery is charged, right?

Go over to Maine Sails site and read some about batteries, or maybe battery university. It takes hours to top off a battery, there is nothing you can do to change that, if you do not fully recharge on a regular basis, you can recover some by equalizing, if your batteries allow that, but chronically undercharging is a definite way to shorten the life of your bank.
If you know that and accept it, fine. No problem, just accept a shorter life and move on. I used to replace the bank in my last little boat every other year, I moved them to the RV for two years, and then they were traded for new. I didn't worry about three stage chargers, battery monitors, external regulated alternators and all the other stuff, I merely replaced the small bank every other year and never had a problem.
But now I have a much larger bank, an expensive bank, and I want to make that bank last as long as possible, as opposed to buying a new couple of grand bank every other year.
Actually I hope to make it last long enough so that LIFEPO is mainstream and no longer a science experiment, I hope not to buy another LA bank.

[Adelie]

Originally Posted by a64pilot

If you have an unlimited charge source, say a Megawatt Solar array, and 1 100 amp lead acid that is discharged to 50%, it's going to take a min of five hours to fully recharge it, add a little age to that battery and it takes longer, the further you discharge it, the more time you add to fully recharge.
Yes I know many who say their bank is fully recharged by noon, you know the little green light comes on and their battery is charged, right?

. . .

From 50% DoD it's more like 6-8hr to 100%. You can shave time off the first 25% of recharge by pushing a lot of amps but that last 25% is going to take 5-6hr regardless of whether you use solar, wind or alternator/genset. A getset/alternator charging to the 100a-hr battery doesn't make sense in any way, shape or form once bulk charging is done at 25-30% DoD. From there the battery is accepting 5amps or less for an extended period. A 75w panel could handle that. For that matter a 75w panel could do the bulk charging from 50% to 25% DoD in about 4hr. As long as you have at least 10hr days you should be able to fully recharge a 100a-hr battery daily with 75-100w of panels.

Folks that don't draw much overnight may be able to get back to 100% by noon. If they are at 20% DoD at 0700 when the sun comes up then there is no reason they couldn't be back to 100% by noon. Starting at 20% DoD they are already part way thru absorption.

[thinwater]

Fun to watch. A few things that may not have been touched on:

• What is a pound of weight savings worth? I'm pretty sure that some posters give it zero value. I like a fast boat and give it about $10-20. So no, I do not want to oversize the bank.
• Replacing batteries varies in complexity. Mine are in the bridge deck lockers, which is nice in terms of venting and access. For me it is easy, perhaps 1-hour including lugging.
• I don't like 80% DOD because I need a cushion. The one inescapable argument against 80% DOD, IMHO, is the risk of going much lower if something is miscalculated or a mistake is made. The kids leave stuff on. Anything.
• In cold weather voltages are lower, and this time of year anything below 50% DOD courts low voltage cut-outs. Not always bad (better than damage), but something to consider. I like that my inverter has an adjustable cut-out.
• Mistakes happen. I've heard a lot of stories about a gold-plated battery being ruined by one mistake.

So I keep a relativity small bank, good solar, and turn stuff off before I hit 50%. Cheap, light batteries last 5 years. But I am also sure that this is NOT the right answer for a monohull live aboard. Why does it have to be one-size?

[Stu Jackson]

Originally Posted by a64pilot

Yes I know many who say their bank is fully recharged by noon, you know the little green light comes on and their battery is charged, right?

Go over to Maine Sails site and read some about batteries, or maybe battery university. It takes hours to top off a battery, there is nothing you can do to change that, if you do not fully recharge on a regular basis, you can recover some by equalizing, if your batteries allow that, but chronically undercharging is a definite way to shorten the life of your bank.

It's always refreshing when someone posts who has actually done his homework, like a64 and a few others here.

Why Going Into FLOAT is NOT Full

Why Going to Float is NOT Full

[chala]

Originally Posted by kmacdonald

What brand of batteries?

I like Delco for their low self-discharge. I am testing Exide now. Dual Purpose 27SMF.

Originally Posted by kmacdonald

Do you always recharge to 100 percent.

No but the batteries are equalized frequently.
The lower voltage batteries get recharged first automatically until a certain time or voltage, then all the batteries get recharged.
The ability to supply 80A of recharging power to each lower voltage 93-97Ah battery means that the batteries are fast charged.
Apparently fast charging provides the benefit of more cycles.

“In other words, fast charging will give you more cycles than staying below C/3!”

Fast charging of sealed lead acid batteries, SLA, VRLA batteries can be charged fast.