What Would You Choose / AGM or Lithium for House Bank?

[Buccaneer]

I have a choice to make: Dry AGMs (for about 100 amp hrs) at a reasonable cost; or Lithium (for about 600 amp hrs) at an extraordinary (to me) cost.

I have a 1988 70 CPMY. It has the 'standard' mini-fridges on flybridge, & back deck, an icemaker on flybridge, and an EU sized fridge in the galley. 6 self-contained AC units. Starlink and the typical electronics package. NO Seakeeper gyro (at anchor) stabilizer. I plan to live aboard and cruise the boat up and down the east coast (Maine-PEI to Bahamas, FL Keys) for the next five years, anchoring-out about 30% of the time. There are 20 and 12.5 kW generators aboard.
I could use the boat as Hatteras seems to have designed it, as a "genny" boat, and not set up a robust inverter system for the house; or I could refit it with a robust house-bank. I'm not a big fan of lithium batteries (because of the apparent inherent dangers) and yet am told that the newer "smart" inverter/chargers have taken away most/many of the underlying problems. The benefits of lithiums (fast charge, deeper depletion ability before recharge, larger amp hr capacity per square foot of space) have nudged me closer to "they'd be a better fit for what I want to do."
I am fortunate in that I can afford to do either set up.
It is also clear that fuel to run the gennys is a LOT less than the cost of the battery bank over that same 5 years.

Which would you do, and why?

 

[Pascal]

I am about to install an inverter system on my 53 since we re about to move it to TN where AC won’t be needed as much.

I m going to with a smallish inverter (3kw) for the fridge, Starlink, a few lights etc. For batteries I m going to stick with lead acid golf cart batteries. They re true deep cycle and will be reasonably accessible so topping them off every couple of months is no big deal.

In my experience, AGMs do not last longer than lead acids.

As to lithium, I m not a fan. Yes some types are safer than others but most seem to be made in china and there have been way too many fires were lithium batteries were the prime suspect.

Space and weight isn’t much of a concern on our boats so I just don’t see the need for lithium. And will they last much longer than lead acid? The jury is still out on that one.

 

[cww]

I only have a 53 with one gen, but the former owner installed an inverter system and dedicated house bank (of AGM's - he was vocal about not liking lithium batteries because of the well-known fire risk). The reality is it's a waste of money - I never use the inverter. He lives in Northern VA, so you don't need a/c for half the year. I'm in Florida, so whenever I'm off the dock I have the generator running because I have the a/c's going. I think that's what it's always going to boil down to, a/c vs. no a/c. If you want to run the a/c's there is no way you can get a battery bank big enough to make that work sensibly vs. running the generator, it would cost a fortune, weigh a ton(s), and would discharge quickly. As long as you're going to have to run the generator much of the time anyway if you want to have a/c, personally I feel like the inverter thing is wasted money, weight, and space. If you live in Alaska or Nova Scotia or something it might make sense, but you're talking about Florida and Bahamas, you're going to spend a ton of money and still use the generator most of the time.

 

[Pascal]

Well with my original invert set up years ago, there were many days from October thru may when AC on the hook wasn’t needed during the day because of the constant breeze and the excellent ventilation of the 53.

At night depending on the weather i would have to run the AC in the master.

Summer? Yes AC is needed

Back then the inverter and batteries paid for themselves in about 18 months in fuel savings alone.

 

[drewread]

I have a choice to make: Dry AGMs (for about 100 amp hrs) at a reasonable cost; or Lithium (for about 600 amp hrs) at an extraordinary (to me) cost.

I certainly don't want to steer the discussion away from this forum, but Trawler Forum's Electrical and Electronics section has some excellent discussions on the benefits of switching to Lithium banks. I've been following a few of them quite closely and there is a lot of great reading to be had there.

It is certainly a hot topic at the moment as there are a number of active threads on the first two pages.

Perhaps scoot over for a quick read, then bring the discussion back here and steer it more towards the Hatts.

 

[warrenw]

I have 800AH of LiFePO4 for my house/inverter bank. I installed this system in early 2023 and after living with it for 2 boating seasons I would never go back to FLA or AGM for house or inverter loads.
I do have the house setup such that I can switch it over to the engine start FLAs in case I ever ran into an issue but I have experienced no issues with these LiFePO4 batteries, they just work and require no maintenance.
LiFePO4 batteries have so much more usable capacity per rated AH and they hold their voltage above 12.6V until they are almost fully depleted. They also have a very reasonable self discharge rate for those of us who winter store outside. For example, this photo was taken when I turned the system back on April 12th, 2025 after being shut off during winter storage (system last charged Nov. 9, 2024).

Prices of the LiFePO4 batteries have dropped so significantly over the last few years. If you want to buy, get them ASAP before US inventories are depleted and new units ship from China with tariffs, as the unfortunate reality is that ALL LiFePO4 cells are made in China regardless of where the batteries are assembled.

 

[Boatsb]

I'm sure the facts should be considered.

1) Systems can be and have been designed to run AC (Air conditioning) on theese and other boats effectively. I've done this a hundred times. Literally.
2) LiFePo4 batteries are not subject to thermal runaway and fire.
3) Usable energy density is 5 to 6 times with LiFePo4.
4) Charge efficiency is considerably better with LiFePo4 although they do not need to always be 100% recharged.
5) Properly designed and implemented systems with correct BMS integration is not an insurance issue. Understanding the technology is key.

I'd hope those who have not learned the facts would allow those who have to come in and correct the misconceptions. Too often opinions are stated as facts.

 

[Captain Ralph]

K I S S
Sorry, but this may have great meaning here.

 

[Addie-Kat]

Here are fact’s, I’m just trying to state answers to some of the questions i was interested in when choosing the type of system i was going to install.

** I’ve had 990 amp hours at 48 volts on my boat for 4 years now, 20kw Victron system including victron liFePo4 batteries.
** I have solar panel’s, they are nice, they help while sunny, but not needed.
** I do not regret for one minute spending the money on this system, and have not had one issue with it,
** Yes, it was expensive to install, but what isnt when it comes to Boating.
** You will not get your money back from the cost savings of not having to run your generator 24 hours a day, but you will save a ton of money on Diesel. However What is Priceless, is the complete silence while at anchor while still having the air conditioning running.
** The amount of usable power in a LiFePo4 battery cannot compare to a lead acid or AGM Battery, This is why you can run air conditioning on a lithium bank.
** With my system I can run the salon air conditioning all day long as well as well as everything else on the boat excluding the other air conditioning units and then charge the batteries before bed for 2 hours and the battery bank will be back to 100%.
** I can operate 3 state room a/c all night long and wake up in the morning with 40% battery life left.
** I have cut my generator usage down to 4-4 1/2 hours in a 24 hour period and sleep in total comfort.
** Neither, the batterie's, nor the cables get hot or even warm while in full use or receiving over 240 amps per hour while charging
** I am very glad i spent the extra money and went LiFePo4 and not agm or led acid for the house bank.

Maybe this helps Maybe not, but these are all Facts

 

[Addie-Kat]

Oh one other comment,

Even the golf cart companies are now choosing lithium Batteries

 

[SKYCHENEY]

AGM's would be my last choice. I have never had a good experience with AGM's. Over the years, I have had wet lead/acid and Gel Cells, and both did the job, but every AGM I had died early. Never again. I won't buy them.

 

[carolinacoast]

Isn't there an ABYC requirement for special boxes to house Lithium Batts along with a BMS?

 

[Timeless72]

Here in the northeast, we use a 5k victron with AGMs. I have enough to power an icemaker, two fridges, and anything else we want throughout the day. Solar keeps bank around 90% with a dip to roughly 65% in the AM. We run the genset a couple hours each morning for laundry, hot water, and recharge. 50 hours or less each year on the genset. However, we do not use AC much while on the hook. All that said, I love not hearing the noise or smelling exhaust while swimming, etc. Happy with everything so far.

 

[scottinsydney]

Five years ago we installed a 5K Victron inverter charger and 20Kwh of lithium batteries. 1200w of solar. Boat on a swing mooring.

The big refrigerator has never been turned off. We have 240 and 120v circuits thanks to Victron Autotransformer.

Five of the seven aircons can now be run from the batteries. Typically we run a 12K and 7K aircon on hot nights.

Watermaker now makes water for free. Washing machine / stove / oven all run off the inverter.
No genset noise. No maintenance.

Genset run time reduced from 600 hours per year to 200 hours per year. Now its primary use is for charging batteries, heating water or running the 24k salon aircon when its hot.

1200w solar on flybridge roof is only adequate. 2400w would be ideal.

The boat now operates as a house would. My only regret for our size boat is not choosing an 8k or 10k inverter charger. 5k is too small and too slow to charge.

Take the plunge and do it!

 

[Buccaneer]

I see that this question is something like "Which is the best anchor?"
Interesting points from all. My thanks for your input.