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Old 14-03-2019, 04:07   #1
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Battery maintenance

Lifepo4 look excellent.* Expensive but an easy battery to use.
Ideally stored at 4℃ with 40% charge when not in use provides a higher probability of maintaining their performance hence increasing their lifespan.
They can withdraw up to 80% of their power without instability of long-term chemistry.*
I use them at home a lot.* I have a bank of four small lifepo4 to power a small tool.* Because the bank would last over 2-3 months I get lazy.* A compromise.* Like sailing into the wind.
I keep the 3 unused batteries in the fridge.* Rotation occurs when I guess the tool is half flat.* When all 4 are flat the rotation cycles again.
On a boat as house batteries?* I would have an isolation switch for each battery in the bank.* I'd probably use them as a team and set a low alarm at 30%. An easy battery.* Recharges fast.* Longer life on a middle rate float then that of full charge or flat.* Flat not good.
Disadvantage is that the cells are not naturally uniform.* They are externally managed.* I do not know how to fix a broken lifepo4.
Glad lithium technology isn't as explosive now.* They're wow.

AGM deep cycle is my favourite.* Cheaper.* Cells are uniform like water.* But unfortunately they are known to have shorter lifespans although I believe such is due to neglect.* AGM do not charge as fast as lifepo4 nor do they allow big withdraws from their power. 50% Max is all you get to use or long-term chemistry will destroy the battery.* AGM (which are basically the same as lead acid deep cycle) benefit from long periods of 100% charge.* They can recover from injury sometimes.
My experience of Lead-acid was using 2 200Ah (guessing)* second hand batteries.* They had failed high current load tests. (Note.* Cold crank amp design,* not deep cycle).* We used the second hand batteries as ballast and deep cycle batteries.* They lasted many years in the vessel and then many many more as house backup during blackouts to provide lights,* tv,* air con.* To achieve 10+ years from assumed dead batteries was simple.* Kept 100% charged and used as per designed to be used.

Looking at a boat now.* Looking at research.* Will probably bank AGM.* Here is why.

4*100Ah lifepo4=$2500
A beautiful choice to use if never ashore hence the charge level bouncing between 30%-100%. Hit 30% and get it up.
Usable Ampere hours =280 AND a highly efficient charge acceptance.

8*75Ah gel cell AGM=$1200
4*175Ah gel cell AGM=$1050
I'll be on shore power all but 4 weeks a year.* 100% available charge.
At sea.* Probably bank them.* Leaving 1 bank at 100% will the other bank loads.* Switch.* 2 days maintaining 100% or 60% level. (40% withdrawal).* Whichever occurs first. That should last longtime.*
600Ah = 320 usable Amphours.* Yes there is more available but how often do vehicles touch their red line?
700Ah= 360 usable Amphours.

If using fossil fuel generators,* the AGM will cost more to recharge than the lifepo4. If with abundance of energy than the lesser efficiency of the AGM wouldn't hurt the bill of upkeep.

Retiring in 15-20 years.* Might even switch to lifepo4, the new saltwater battery or whatever available then,* then.

I hope that's helpful.* Basic understanding makes easier maintenance.
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Old 14-03-2019, 04:16   #2
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Re: Battery maintenance

I failed mention.. AGM don't like high currents.. High currents tend to destroy them
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Old 14-03-2019, 04:25   #3
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Re: Battery maintenance

If a discussion warrants a multicultural battery system. Include me.
Figuring at moment how one could incorporate a 200Ah lifepo4 banked with a 175Ah AGM.
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Old 14-03-2019, 05:13   #4
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Re: Battery maintenance

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Originally Posted by Boatsie View Post
AGM deep cycle is my favourite.* Cheaper.* Cells are uniform like water.* But unfortunately they are known to have shorter lifespans although I believe such is due to neglect.*

8*75Ah gel cell AGM=$1200
4*175Ah gel cell AGM=$1050
I'll be on shore power all but 4 weeks a year.* 100% available charge.

Our oldest bank of AGMs lasted 12 seasons. The second oldest is entering 10th season. That's with near-daily access to shorepower, though, and with a generator I'm not afraid to use... with occasional anchoring periods only a few days or weeks at a time.

From reading, I don't think "neglect" is always the perfect word... since that also implies lack of interest, laziness, not paying attention, etc. In some cases, cruisers -- away from shorepower -- who try to treat their batteries as best they can... just can't recharge to full enough often enough. Those with solar probably do better.

gel and AGM in the same sentence is incorrect.

Lots of threads here on lithium, AGM, etc. Check out posts by Maine Sail...

-Chris
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Old 14-03-2019, 05:49   #5
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Re: Battery maintenance

Cheers Chris.
I'd thought Absorbed Glass Mat consisted that of gel.
My ignorance.

AGM reads much better than a gel cell as per boating usage.

AGM
Slightly more tolerant. Can handle short bursts of current. Not as strict with recharging as a gel cell.

Gel cell. Very high score at slow discharge usage. Very strict with recharging though or prone to premature failure. Handles a higher ambient temperature than an AGM.

Thanks
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Old 14-03-2019, 06:02   #6
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Re: Battery maintenance

My figures are way out too.
40% of 700= 280Ah

I had 4 years from an AGM on mind..
Was thinking someone might have done what my mate did.. Eg he refused offer to give his battery a good charge and then insisted that the battery was at fault, not being able to remain dead until he wanted life out of it.

They love staying charged.. Lithiums are like athletes.. They love lazing around at half charge. Neither survive being dead.
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Old 16-03-2019, 12:02   #7
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Re: Battery maintenance

I'm probably not correct above.
A trusted expert told me about 40%4℃ lithium but the 2 lithium batteries I used were usually charged and then recharged when about half flat. Same age.. But the one left low on charge for months didn't recover whereas the battery left high on charge is still in service.
They confuse me.. I'll stick with basic batteries because of such. I have no idea. Thanks for helping me understand above..
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