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Old 08-10-2021, 11:16   #1
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Question AGM to LiFePO4; can I replace my starting battery, as well?

Hello all,

I'm doing a bunch of upgrades to my boat and BATTERIES are my next thing. I was reading this article:

https://www.deepcyclesystems.com.au/...oat-batteries/

It's an article about a Jeanneau 39 (very similar to my Jeanneau SO409; or maybe identical?) and how they went through an upgrade to lithium.

My poor attempt at my current diagram:



And this is my mess of a boat:

AFT PORT:

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AFT STARBOARD:

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So my question is - can I replace ALL of them with LiFePO4 batteries? My Cristec battery charger has the option to charge them correctly:

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BUT...

Can I use a LiFePO4 as a starting battery? I'm assuming the one on the upper left (left one under the AFT STBD mattress) is the engine battery.

I don't know why this is confusing me so much. I did so much research over and over again...

I'm debating between:

Battle Born 100 Ah 12V LiFePO4 Deep Cycle Battery
https://battlebornbatteries.com/prod...cycle-battery/

or

ExpertPower 12V 100Ah Lithium LiFePO4 Deep Cycle Rechargeable Battery
https://www.expertpower.us/products/ep12100-100ah

Budget is $3000-$4000. Looking for it to be as easy as possible. A simple swap would be awesome!

So, my question(s) is/are: (1) Can I replace all 5 to LiFePO4? If not, then (2) Can I replace the engine with AGM and the 4 domestic with LiFePO4?

Any help will be greatly appreciated!!
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Old 08-10-2021, 11:23   #2
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Re: AGM to LiFePO4; can I replace my starting battery, as well?

Just wanted to add the back of my battery switch panel:

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Old 08-10-2021, 12:21   #3
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Re: AGM to LiFePO4; can I replace my starting battery, as well?

https://marinehowto.com/lifepo4-batteries-on-boats/

Best lithium help site I know.
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Old 08-10-2021, 12:27   #4
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Re: AGM to LiFePO4; can I replace my starting battery, as well?

Quote:
Originally Posted by Nicholson58 View Post

Thx for reminding us of that link.


Now we just have to get 'em to read it and heed it.


I've been dealing with that issue for 20 years on our boating website and forum. And even if they read it...

Finally, at a member's suggestion, we called one thread: CRITICAL UPGRADES - Do This or Else!

Still get folks asking if they should...
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Old 08-10-2021, 13:55   #5
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Re: AGM to LiFePO4; can I replace my starting battery, as well?

The previously linked marinehowto site article is required reading. But, keep in mind it is only one (very well informed) opinion.

1. Take note that it is often desirable to leave a lead acid starting battery in place and parallel that to the LFP while charging.

2. Take note of extensive alternator upgrades usually necessary if you don't do 1.

3. Take note of charging requirements, and that just because a charger says Lithium doesn't mean it is doing it properly. With no other information than the chart you posted, I guess your charger does not.
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Old 09-10-2021, 08:26   #6
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Re: AGM to LiFePO4; can I replace my starting battery, as well?

So I'm guessing I can't just buy 1 new AGM and 4 new LiFePO4 batteries and just drop them in as a single swap? And here I thought my Cristec battery isolator and my Cristec battery charger were new enough of a technology to just do a swap
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Old 09-10-2021, 08:56   #7
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Re: AGM to LiFePO4; can I replace my starting battery, as well?

In my experience, an isolated lead acid starting battery is still ideal. They are much better than lithium as a cranking battery, and its good to have it lead acid if you are crusing, you can get a car battery anywhere. Love my lithium, but not as a starter bank.
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Old 09-10-2021, 09:32   #8
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Re: AGM to LiFePO4; can I replace my starting battery, as well?

I believe the AGM is best to use as a starting battery. You could use a trickle charger from the house batteries to keep it charged (it’s only discharging when you start the engine). I’m sure smarter people will chime in if I’m wrong.
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Old 09-10-2021, 09:35   #9
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Re: AGM to LiFePO4; can I replace my starting battery, as well?

Quote:
Originally Posted by Cool Hand Luke View Post
So I'm guessing I can't just buy 1 new AGM and 4 new LiFePO4 batteries and just drop them in as a single swap? And here I thought my Cristec battery isolator and my Cristec battery charger were new enough of a technology to just do a swap
As Lean says yes you can and an AGM start battery plus LFP domestic batteries is a good combination.

However, I think you need to do some re-wiring once you have sorted out how you intend to charge the LFP batteries. The settings on that Cristec battery charger (shore power) suggest a long absorption if I have read it correctly. That is a no no for LFP.

There are lots of ways of wiring this all up, but assuming you have a standard probably about 70A then the alternator charge needs to go to the engine start battery. You could then have a DC>DC charger to charge the LFP batteries. The advantage of this is that the DC>DC charger limits the amount of current being taken from the engine start battery and therefore alternator to a level it can generate at for a sustained period. If you don't limit the charge to the LFP then they will take all the power the alternator can generate and it will overheat and self destruct. Two popular products to do this are:

https://www.victronenergy.com/dc-dc-...t-non-isolated

https://sterling-power.com/collectio...ttery-chargers

There are lots of others, Mastervolt and Renogy probably have similar products. Size the DC>DC charger to a maximum of 60% of the alternator output rating, no more. Do not put a DC>DC charger under that bunk or in a closed space, they get really hot and need lots of cool air. Picture is a temperature reading taken from my Victron DC>DC charger and its mounted under the chart table with a 3" hole behind it to increase cooling to the fins. It still reaches 60c.

The Cristec battery isolator becomes redundant and should be removed. The Cristec battery charger should be re-wired to only charge the engine start battery. Then the DC>DC charger passes this charge, with limits, to the LFP batteries.

You will need some fuses, extra battery switches and if you don't already have one a battery monitor to see what the alternator is doing.

I would suggest in addition to the Marine How to page, you also spend several weeks going back through the CF lithium power forum to learn all you can about these batteries. I think you could do this within the budget, but you must have a good understanding of lithium before lifting a screwdriver or it could get very expensive, very quickly.

Now what is the reason you want to fit lithium?

Pete
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Old 09-10-2021, 11:32   #10
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Re: AGM to LiFePO4; can I replace my starting battery, as well?

I would not. For two reasons.

1) You would need a BMS that tolerates the amps during engine start. Expensive.
2) The batteries need to be big enough to handle the Amps. For example for the Eve cells I am using max discharge current is 1C. Of course they can tolerate more for a short time, but LifePo4 batteries are sensitive. For Winston cells this would be 3C. Better,

GWL, a company selling Lithium cells and so on are not on board with Lithium as starter batteries.

https://shop.gwl.eu/Technical-suppor...g-battery.html

I use a Lead acid starter battery, with a DC/DC charger to my Lithium house battery. In emergency, I could start the engine from my Lithium, only requires bypassing the BMS and also the DC/DC charger.

The other positive thing about using an (isolated) DC/DC charger is that you can galvanically isolate the engine/saildrive from the rest of the boat
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Old 09-10-2021, 12:16   #11
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Re: AGM to LiFePO4; can I replace my starting battery, as well?

Quote:
Originally Posted by Cool Hand Luke View Post
So I'm guessing I can't just buy 1 new AGM and 4 new LiFePO4 batteries and just drop them in as a single swap? And here I thought my Cristec battery isolator and my Cristec battery charger were new enough of a technology to just do a swap

Have you had an opportunity to read Maine Sail's article yet?
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Old 09-10-2021, 16:51   #12
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Re: AGM to LiFePO4; can I replace my starting battery, as well?

Thanks for all the input and to all that chimed in.

Yes, I did read the article... but still confused, as most people would be (and I went for engineering to school)

I really thought I could just keep the UPPER LEFT (in my diagram) battery as AGM (I would buy a NEW GPL-27T) and then the other 4 batteries would go from GPL-27T to Battle Born 100Ah LiFePO4.

I thought I could do it without rewiring anything... again, the Cristec has a LiFePO4 setting and the Battle Born LiFePO4 batteries ($800 USD each) have BMS built-in. I don't mind spending the money if it'll work properly and I won't kill the batteries in a season or two

So I shouldn't do it, if I don't want to rewire anything?
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Old 11-10-2021, 15:04   #13
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Re: AGM to LiFePO4; can I replace my starting battery, as well?

Quote:
Originally Posted by Cool Hand Luke View Post

So I shouldn't do it, if I don't want to rewire anything?
Correct, leave well alone if you want to keep the existing equipment and wiring.

I assume those Gp27s are on there way out? They could be replaced with GP31s which would increase the available domestic bank. You need to rewire them slightly as the first battery has both the neg and pos wires coming off it. Put one of these on the other end of the bank. That way the batteries will share the load better. Also there is some corrosion on two battery posts , so whilst you are at it clean up the connections when fitting new batteries and add a thin layer of grease.

Pete
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Old 11-10-2021, 19:47   #14
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Re: AGM to LiFePO4; can I replace my starting battery, as well?

Quote:
Originally Posted by Pete7 View Post
Correct, leave well alone if you want to keep the existing equipment and wiring.

I assume those Gp27s are on there way out? They could be replaced with GP31s which would increase the available domestic bank. You need to rewire them slightly as the first battery has both the mast neg and pos wires coming off it. Put one of these on the other end of the bank. That way the batteries will share the load better. Also there is some corrosion on two battery posts , so whilst you are at it clean up the connections when fitting new batteries and add a thin layer of grease.

Pete

Thank you, Pete!!! Will do. Since this is not my last boat (i.e. I'll hate leaving this one, but I'll buy a new one when I retire). As for now... I'll buy 5 new GPL-31Ts to replace my 5 aging GPL-27Ts.

Yes, they're aging... and correct, I do see the corrosion. I'll clean that out and will research on preventative maintenance for my new 31Ts.

Thank you, Pete!!!
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Old 26-11-2021, 16:05   #15
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Re: AGM to LiFePO4; can I replace my starting battery, as well?

I got the GPL-31T batteries. 5 of them. What should I do with the old GP27s? Is there a recycling place I should look for? I am in northern New Jersey.

Are there companies that recycle them? Is there any value in them? They still held charge on my boat for about a day at 4-6 Amp continuous draw.
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