LiFePO4 batteries going mainstream?

[Godot]

It's beginning to look like lithium (LiFePO4 most common on boats) are beginning to go mainstream. The prices are dropping to the point of being practical without breaking the bank.

100 AH SOK LiFePO4 battery available for $570. I saw a youtube review of that battery and was pretty impressed. The batteries appear well built, and are servicable (cells can be replaced if necessary). There are lots of other brands out there as well, some more expensive, others less. Battleborn is a common brand, and is a lot more expensive; but still, even there the price is coming down.

It's getting to the point where I think I'm going to be able to justify going this way when next I replace the batteries in a year or so. 200AH lithiums replacing my 200AH FLA cells would pretty much double my useful capacity.

Advertised advantages: Lighter weight than Lead Acid batteries, and the ability to take a much deeper discharge without damage. I think many battery manufacturers claim a 100% discharge rate; but my understanding is that 90% is a better point. Many batteries apparently turn themselves off when they get down to 90% DoD in order to protect themselves. They can also take a much larger charge source (apparently 50% of the rating); though I suspect most of us in small boats won't have a charge source that can provide that much juice.

Disadvantages that I'm aware of: They can't take a charge when they are below freezing without serious damage. Some batteries, at least, have a temperature disconnect to protect against this. There is also some fear of fire, although I don't think that is a big thing with LiFePO4. They are more expensive initially, although maybe that isn't true anymore if you compare usable capacity per dollar of AGMs compared to usable capacity per dollar of LiFePO4 especially if you consider charge cycles. I also understand you can fry these batteries fairly quickly if charge controllers aren't set up properly, so the cost of new chargers might need to be factored in. And lastly, I don't think you can really tell state of charge via voltage, so a battery monitor that understands lithium would probably be a good idea.

I've been trying to understand what would happen in a mixed environment. Right now I have two FLA battery banks that link together by an automatic charge relay when there is a charge source. If I were to go LiFePO4 for the house bank, and keep a smaller lead acid for the starting battery it's not clear to me if it would be OK for the two batteries to link via the ACR during charging. Actually, I'm not sure the ACR would ever disengage even when not charging given the voltage cutouts, and the two banks could be linked together most of the time which might not be good. I've been told by some folks that LA is better for starting, and by others that it would be OK to just use the house lithium bank for starting maybe allowing the removal of the starter battery.

[Norman]

Thanks for the extensive over view.

The built in protection from going below 10% is vital, near zero, they can not be recharged.  I have been there with a laptop.

Charge controllers and chargers must be exactly matched to the size and nature of the bank you buy.  Lithium batteries vary in the manner in charging they will accept without damage.

Any  device that can co ordinate charging both technologies lead and lithium, from a single source would be out of sight expensive, dedicated separate is the way to go.

Tying them together temporarily would most cheaply done with a mechanical switch, returned to open as soon as possible.

I agree that the fire danger has been addressed in most designs, but  I believe that a quick disconnect system for the wires, and quick release for mechanical security would be well worth designing in to the installation.  This should make it possible to remove the battery if trouble is detected.  My understanding is that smoke is present for quite a while before fire is likely.

Certainly the power density per pound is extremely attractive, and discharge to 10% without damage allows a much smaller AH for the same service.

[Owly055]

I've lost several lithium batteries (cordless power tool) due to temperature extremes.... how this equates to LifePO4s I don't know, as the chemistry is different.  It seems that most lithium batteries are "intelligent" in terms of limiting charge and discharge... The technology is just too complex not to have onboard control.

[curtis]

LiFePO4, aka LFP, lithium iron phosphate, is not flamable.  You can put it into an incinerator and it will burn and take it out and it will go out.  LFMP, lithium iron manganese phosphate, adds some manganese and gets better density, weight and volume, and cost, than LFP while being nearly as non-flamible.  Anything with cobalt or (less so) a lot of manganese in it tends to be more flamible, NCA (Tesla), MNC (most other high end BEV), and others like Nissans older LMO.

Batteries can be bought as cells with separate BMS (battery management system) which is the cheapest way to go but unless you are an engineer and really want to put effort in configuring then not worth the savings.  Then there are batteries that include a built in BMS.  These are more expensive but well worth it.  Since they have built in BMS they are tolerant of  high charge voltage (to 15.8V for ones I bought).  You still need a charge controller for solar (can go over 17V) or for other charge sources but you can set abosorbtion voltage to float voltage (at 14.4-14.6V for the ones I have) and unlimited float time since the BMS will stop the charging when full.

Some sources (with BMS) are Battle Born, Rensys, and Lithium Battery Power.  I bought from LBP.  Prices have gone up since I bought (cell prices must be up or something).  I suggest the LBP eco rather than premium series if you don't care about CCA over 1000A per battery (premium can peak at 2500A for 5 seconds) or other high discharge capability.  Ask LBP what the difference is (I just checked spec sheets) as cost is quite different.

Weight is 1/4 to 1/5 of lead acid.  I have 12V 100Ah at 27 lbs each.  Volume is also smaller.  Cost is higher per kWh vs AGM but batteries with BMS are rated at the amount the BMS will let you charge to (not 100% of what the cells can take) and what the BMS will let you discharge to (typically 15-20% of cell capacity).  So you can use 100% of the capacity where lead acid you typically use under 50% to maintain battery life.  So while cost vs AGM may be 3x considering you can use 100% capacity with good longevity its 1.5x comparing usable capacity.  The Li-ion batteries will last many times longer than AGM so in the long run are a better deal.  Also lead acid sulfates if left partially charged for even periods of days.  If you plan to rely on renewables which bring back charge on a large bank over the course of days then you have to consider the shorter life of lead acid in that use.  If you charge 1-2 times daily then lead acid longevity is not reduced if you don't discharge deep.  In that case you just wear out the diesel by idling for long periods with almost no load.

You can leave Li-ion batteries for long times without charging (best left at 50% SoC) where lead acid with high self discharge will self destroy.  I've talked to boat owners who replace batteries every 2-3 years because the boat are stored a long time (one in the tropics).  They would be better off with Li-ion due to the longevity but keep buying AGM or wet cells.

Old thread but still relevant I hope.  btw- I'm repowering with electric auxilliary and bought a total of 20kWh of Li-ion (24V 75Ah and 12V 100Ah).  This would be a lot of weight in lead acid but not bad in Li-ion (under 350 lbs total).  And hopefully they will last.

Curtis