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[Noah]

Overkill. Mine cranks-up instantly with a flooded group 24 Penn 650 battery with 550 CCA.

[waughoo]

I used a group 78 side post battery for my dedicated start battery.  The shorter and larger wire runs made a noteable difference in cranking performance (mounted under the aft berth).

[senorquill]

I used a group 78 side post battery for my dedicated start battery.  The shorter and larger wire runs made a noteable difference in cranking performance (mounted under the aft berth).

Waughoo,

I like the sound of that set up, do you have photos of that placement? Are you using a charger relay, or is the starter battery its own bank?

Sound like a good way to get a third House Battery under the saloon seat.

V/R,

MQ

[waughoo]

I used a victron dc to dc charger from the house bank to the start battery.  All my charging sources go to the house bank.  I elected to go with the side post battery so I could fit it easily under the aft berth.  It is just opposite the vertical wall at the aft end of the footwell of the aft cabin.

I do have photos but none handy at the moment.

[Jim Hardesty]

Here is a webinar on lithium batteries hosted by the GLCC School that may be of interest.  (Great Lakes Cruising Club)
https://www.glccschool.com/content/mx00102-h-lithium-battery-technology-cruising-boaters
Watch live and ask questions, then next day get a link to the recording for review.  I've found the GLCC webinars to be very helpful.  Many more topics than the battery one.  FWIW my favorite is the weather webinars, I now can read and interpret weather maps.  Have much more confidence in cruise planning.
Jim

[senorquill]

I used a victron dc to dc charger from the house bank to the start battery.  All my charging sources go to the house bank.  I elected to go with the side post battery so I could fit it easily under the aft berth.  It is just opposite the vertical wall at the aft end of the footwell of the aft cabin.

I do have photos but none handy at the moment.

Thats make more sense to me, to send power from the house bank to the starter, since it would only be a small amount to top it back up. My stuff is arriving today so i'm going to start the install.

Please send the pics when able.

V/R,

MQ

[waughoo]

Here are some photos.  Built a custom shelf epoxied to the hull to hold the battery in the aft area.  There are two vertical walls port and starboard that serve to corale the battery and provide mounting surfaces for the fuses, RBS on one side and the victron B2B on the other.

[waughoo]

After it all got wired up, I removed the 1 2 Both switch replacing it with the switches for the RBSes (one for engine start and one for house panel).  The switch on the far right of that panel is for my mast head tri color/anchor/strobe.  The panel breaker for anchor turns it on and the three way switch shown closes its function.

[waughoo]

With regards to the charging power all going to the house bank, I MUCH prefer this to the other way around.  If one increases their alternator charging amps and they have it going to the start battery, more B2B chargers need to be added to take advantage of that extra power.  The start battery really only needs a small amount after each use.  I went with an 18 amp B2B as it was a bit cheaper and honestly, unless the battery was COMPLETELY dead, I will never get to a full 18 amps.

Putting alt charging direct to the house does also require a high quality remote regulator that has the ability to specifically set the charge profile for lithium and monitor alternator case temps, but any good house bank charging system should be remote regulated for a boat that is meant to spend multiple nights away from a dock.

Let me know if you have any questions about the set up.

[mainesail]

This article while very long has all the details you are looking for.

https://marinehowto.com/drop-in-lifepo4-be-an-educated-consumer/

[senorquill]

Lithium bank installed with separate AGM for starter. Today I'll add a Positive Bus for the House bank and then install the DC to DC charger. So far it's all working. I'm planning a 4 day sail this weekend to test it all out. Looking much cleaner than before. If I were to move the starter battery to the Aft Cabin I could fit 4 Lithium's in the current house bank location. Only issue is those batteries are $650 a piece. But right now I have essentially twice the power in the house bank with those 2 Lithiums.

[senorquill]

After it all got wired up, I removed the 1 2 Both switch replacing it with the switches for the RBSes (one for engine start and one for house panel).  The switch on the far right of that panel is for my mast head tri color/anchor/strobe.  The panel breaker for anchor turns it on and the three way switch shown closes its function.

Waughoo,

That's a nice setup. Have you had any issues with moisture in that location? I typically have water sitting back there due to the stuffing box and general condensation.

MQ

[waughoo]

I did have some standing water back there in the past but have since drilled a limber hole under the engine pan to get the water to transit forward to the main bilge.  I also have a dripless shaft seal so what is back there is fresh water.

[mainesail]

I’m going to venture forth with my opinions on this subject even though some may not agree.  I’m right in the middle of reconfiguring my boat’s battery and charging systems to incorporate LiFePO4 for the house bank.  My recommendations to MQ are as follows:

1.First, spend some more time educating yourself about incorporating Lithium.  As Maine Sail says, Lithium is not a drop-in replacement for lead acid.  There’s more to consider than you see at first glance.  I’d recommend watching the video seminars on YouTube from Pacific Yacht Systems (Jeff Cote) on the subject (yes, I know, he’s long winded, but there’s good information in there.)  Also Maine Sail has several good write-ups, as well as Nigel Calder’s extensive writings and his videos on YouTube.

2.One of the above authors made a good analogy, which was that LiFePO4 batteries are like marathon runners, and lead-acid starter batteries are like sprinters.  Starting an engine requires a sprinter – big push for a short duration.  This is not what LiFePO4 batteries are designed for.  They are good at providing a strong, steady output for long periods of time.  The three authors above all seem to agree that using a LiFePO4 battery as a starter battery on a regular basis is not recommended. 

3.You mentioned that you were going to have the DC to DC charger charging the starter battery from the house bank.  In my opinion, that’s backwards.  Unless you are also using solar, the DC charger only comes into play when you are charging via the alternator.  When you crank the engine, you are only draining the starter battery by a couple of percent in most cases, unless your engine requires some serious maintenance. (This is why most internally regulated alternators have a VERY conservative charging profile – it only takes a few minutes to fully recharge the starter battery.)  So to me, it makes more sense to have the DC charger look to see when the starter battery has 13.6 V on it (i.e. it is being charged by the alternator), and draw from that side to also charge the house bank, which will likely be in more need of charging. The starter battery will be recharged in short order, and then the DC charger and alternator can focus on the house bank.

4.There are many misconceptions about Lithium batteries – especially the issue with flammability.  Maine Sail does a good job of putting this to rest (as does Nigel Calder), clarifying that the LiFePO4 battery is very different that the earlier Lithium Ion batteries that made the news so often.  The primary concern for fire with LiFePO4 would actually come from situations where a dead short in wiring occurred that would allow the battery to pump out vast amounts of current, melting the wiring.  However most of the batteries being sold today have battery management systems that would shut down the battery in these situations.  That BMS, combined with an appropriate Class T fuse in the main wiring configuration should greatly reduce this risk.  The other situation to guard against is using a 1/2/both switch and combining a heavily discharged starter battery with a fully charged LiFePO4 bank.  The large voltage difference would cause a big current spike, and again could lead to a wiring meltdown. In my configuration, I’m using a keyed switch hidden away from passengers that will allow me in an emergency use my house bank for starting the engine, but only after I first pull the fuse on the starter battery so that the two banks are never linked.

That’s my nickel’s worth.  Is it worth installing LiFePO4?  I think so – for nearly the same cost as replacing my 4 dying Trojan T-105’s I’m getting about 220 amp hours, of which I can actually use about 175 AH on a regular basis (and more if I really need), whereas the Trojans gave me 420 AH, but I could only use about 35% of that on a regular basis or 147 AH (sometimes 200 AH if I pushed it hard, but you pay a price in longevity for that).  Not to mention the far longer lifespan for the LiFePO4.   And I can fit the two lithium batteries easily into the battery box, with enough room to also mount the DC to DC charger in there and do a nice, neat wiring job for my main unswitched bus, fuses, etc. 
OK – I’ve stepped down off my soapbox…

Tom,

Thanks for the great advice. After a ton more research and contacting Renogy it sounds like the 100A a LiFePO4 produces will not work for engine crank ups, so I'll be going with a 2x 100Ah LiFePO4 House Bank and 1x 105Ah AGM starter bank with DC to DC charger option from the starter bank to the house bank.
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I've been watching Pacific Yacht Systems and that's where I got the idea for the DC to DC charger. You are correct about the DC to DC going from the Starter Battery to the House Bank, I miss spoke. That's is what I intend on doing. I have 200 watts of solar also, which I could re wire to the starter battery in the event the alternator craps out and I need the starter battery at full power.

MQ

The best value in a 100Ah drop-in right now are the Epoch LFP Batteries. Amazing build quality a 1.2C continuous BMS(200A for as long as 30 seconds OR 285A FOR 1S), waterproof, BLUETOOTH BMS, cell compression, CAN etc.. Kilovault are also Excellent. You could not pay me to install or own anything Renogy. Way higher than average failure rate but that is not the worst of it . Their customer support is the worst I have seen in any industry. We used to install customer supplied Renogy products to help our customers save money. We had to stop offering this as we were getting blamed for the failures and not a single one had to do with the installation.. I don't think a single customer got their warranty covered...