LifePO4 is tremendous technology but this technology comes at a price.
#1 OVER CHARGING:
LFP batteries will be quickly compromised or DESTROYED if over charged. Unlike lead batteries over charging does not just boil off electrolyte it can cause the case to swell and the cells to be irreversibly ruined.. A lead acid battery will suffer some permanent capacity loss from chronic over charging, but will survive this, an LFP battery WILL NOT. Over charging LFP batteries WILL result in a huge hole in your wallet! This means proper charging and a BMS system to ensure over charging can not happen.
#2 OVER DISCHARGING:
Just like over charging over discharging can actually result in a polarity reversal and destruction of the cells. A lead acid battery may suffer some permanent capacity loss but can easily survive this, an LFP battery WILL NOT. Another HUGE WALLET DENT and another reason why an LFP system is designed and installed as a "system"..
#3 CHARGING BELOW FREEZING:
LFP cells should not be charged at temps below 32F. They can be used below these temps but NOT charged. Lead acid could really care less. Another way to DENT YOUR WALLET!
#4 CELL BALANCING:
Keeping the LPF cells balanced is of prime concern because it is high or low voltages that ruin LFP cells. In LFP cells we have what are referred to as the upper knee and the lower knee. What the heck is a "knee"?
The upper and lower knees are where the battery or cell hits full/empty and the voltage shoots for the moon in hockey stick fashion or sinks like a rock. Over discharging and over charging is where most LFP cells are destroyed. One minute the bank is taking massive amounts of current and the next one cell has gone full/empty and hockey sticks before the other cells.
If one cell becomes out of balance it can hit full before the rest of the cells does and this one cell can be ruined. Cell balancing is most important & most critical when pushing high charging voltages, which IMHO and experience is 150% UNNECESSARY. Charging these cells to more than 14.0V is really 100% unnecessary and only leads you closer into the danger zone, especially if the cells were to drift.. This is why individual cell level monitoring, of cell voltage, is necessary. Pack voltage alone tells you nothing about a cell going off early just what the overall pack voltage is.. A good BMS (battery management system) will cut charging well before any damage can be done.
#5 FLOAT CHARGING:
These are not lead acid batteries, not your fathers Oldsmobile, and they are not designed nor intended to be "float charged" in the typical sense. The only reason people even try to argue this point is because they are trying to save money, cut corners and adapt poorly or inadequately designed lead acid equipment to LFP technology. Not really a wise idea. Look at any of your tablets, cell phones iToys etc. and they all terminate charge when the battery is FULL. They cut back in when battery terminal voltage has fallen to a preset level, but they do not keep feeding current to a full battery.
Floating LFP is a complex subject and I will touch on this later. Bottom line is to avoid floating LFP banks if you can. Some have argued that a float voltage of 3.35VPC or lower (13.4V for a 12V bank) is not badly damaging. Remember this type of charging keeps you in the upper SOC range for long periods of time and these batteries prefer to sit at 50-60% SOC when not being used not 90%+ SOC.. Can you float at 3.35VPC or lower? Sure you can do what ever you want to, but we don't really know the long term affects other than to say it is likely going to shorten the life. Of the 80 or so white papers I have on LFP batteries not a single one of them has dealt with fractional "C" use and floating at 3.35V or lower, not one.
#6 INDUSTRY LIES & MISLEADING MARKETING: Unfortunately most commercially avaible chargers, solar controllers and alternator regulators are of extremely limited design and are NOT well suited to charging LFP banks. Most of these manufacturers have zero, zilch, nada experience with LPF yet they have no qualms making up "Li" charge profiles, despite no physical or practical experience with them. In short many of these LFP charging claims are misleading and can be dangerous to the health of your cells.
PLEASE DO NOT BUY THE HYPE WHEN CHARGER MAKERS TELL YOU THEIR CHARGER HAS A "LITHIUM" CHARGE PROFILE!!!
Many of these profiles can DESTROY your very expensive LFP bank. ProMariner and Sterling Power are two chargers that immediately come to mind with a Li setting of 14.6V absorption and a 14.4V float. The algorithms in these chargers also lengthen the absorption duration> based on the bulk duration. LFP will be in bulk for a long time hence these chargers will hold these insane voltages for far, far too long.
DO NOT EVER use these settings to charge prismatic LFP cells. You will eventually DESTROY your batteries. Here's a hint you DON'T FLOAT LFP BATTERIES. The sheer fact is the people who create these potentially dangerous charge profiles very often have no experience with LFP banks, but, they DO want to SELL you a charger....
On the other side of the coin the Chinese are eager to get into your pants, like a horny prom date. They also MISLEAD and tell you it is safe to charge these banks at high voltages so end users/consumers THINK they can just "drop them in" and off they go. I suspect much of this is simply a misunderstanding between what the consumer wants to believe and what the Chinese actually mean.
Follow me here. If LFP requires different charging and lots of "extras" the conversion from lead to LFP will be MUCH slower and the Chinese will sell fewer cells/batteries. How do they fix this? Hmmm, lets sit in a smokey Chinese factory back room and figure this out.. Oh yeah, I know, just tell them they can be charged at normal lead acid voltages and we will sell more. D'oh..... If I recall the GEL battery makers already tried that and look where their market share is now.
DO NOT TRUST THE CHINESE MANUALS FOR CHARGE VOLTAGE GUIDANCE!!! THEY JUST WANT TO GET INTO YOUR PANTS POCKET AND EMPTY YOUR WALLET!
Let's look at this another way. The Chinese say, in the manuals, it is okay to charge these batteries to 14.4V - 14.6V. Hmmm, what are WE missing? Here it is and it is very simple.. They want you to charge to 14.6V then STOP CHARGING once you hit 14.6V and .05C - .1C current.
The reality is this is not how any commercially avaible marine chargers work. "Charge to 14.6V" is not the same as "Charge to 14.6V and then let it remain charging at 14.6V for FOUR HOURS"...... Are you beginning to see the disconnect?
Please do the research, do your own testing, as I have, you decide, it is YOUR bank and YOUR wallet. I suggest strongly looking at Genasuns's MAX allowable charge voltage. It is 14.2V. This is with a fully gourmet factory engineered system. For a DIY, max out your charge voltage at a 14.0V, and keep the duration to less than 15 minutes at 14.0V, and you will be a happy camper...
You really need to source chargers, controllers and alternator regulators that allow 100% CUSTOM PROGRAMING not some piece of junk wanna-be Li, menu-fed, pre-determined & "selectable" charge profiles made up by a charger maker, who's reading a misleading Chinese spec sheet, and does not understand what it even means. Wow, that was a mouth full...
The previously mentioned ProMariner ProNautic P and Sterling ProCharge Ultra chargers are excellent chargers, for lead acid, because they DO have a custom program feature for voltages only. You could use the custom profile but DO NOT use their "Lithium" charge profile. Where these chargers fall flat, for LFP, is the duration at constant voltage. These chargers lack the ability to shorten the absorption voltage duration so you as a user would need to manually manage that. Where these chargers also fall flat, as most do, is in the lack of a dedicated voltage sense lead. Also the largest charger they make is just 60A. Kind of small for an LFP bank. For a shore charger, a fully programmable unit is better, and by fully programmable, I mean absorption duration AND voltage.
#7 IT IS A SYSTEM, NOT JUST A BATTERY:
An LFP bank is not just a battery it needs to be treated as a COMPLETE SYSTEM. A car is simply not just wheels & a motor and an LFP battery is simply not a battery & terminals unless it has the rest of the system to go with it. This is why drop-in LFP batteries are a complete and utter travesty to me. These "drop-ins" will be the black eye on the industry but many unscrupulous companies will have made their money by then and gotten out...
You read it here and my prediction is this; "Drop in" LFP systems will be the BLACK EYE that may destroy the entire LFP market just like what standard flooded charging voltages did to the GEL battery market.
I HOPE I am proven wrong on this point but it looks doubtful. I have reached out to these companies and tried like hell to get a human being on the phone who had even an ounce of clue about LFP batteries and I failed. Scary stuff... GEL batteries are still the longest lasting of lead acid batteries but they SHOT THEMSELVES IN THE FOOT trying to sell into a market that did not require the "rest of the system". They tried to tell end users to just "drop them in" and they all got fried charging at FLA voltages! DUMB, really, really dumb. Apparently the Chinese have not learned from battery industry history... I won't even bother to go into the why's or how's of why I am not sold on LFP "drop in's" because these companies are nothing more than money grubbing opportunists, IMHO.
When I say system a good system will be designed from the ground up to include a BMS, LFP capable over-current protection, proper cell compression case (for prismatic cells), specifically chosen and 100% PROGRAMMABLE, regulators, controllers and a charge and loads bus as well as LVC and HVC safety cuts. This barely scratches the surface but you can see why none of this is "drop-in".
#8 INITIAL STICKER SHOCK:
Con? Not really but to some it may be.. No matter how you run the numbers LiFePO4 wins the cost per cycle comparison to AGM or GEL batteries. This however does not mean a well designed and engineered system will not have a rather large sticker shock. I don't personally find this a "con", because I am capable of simple math, but some will see this as a con so I mention it.
Do the math on a $$ to cycles calculation and you will see that LFP wins. When doing this math remember that a 400Ah LFP banks has 312-320 usable Ah's when out cruising and you can easily get back to 100% SOC. To get 320 usable Ah's from a lead acid bank, when out cruising, (cycling between 50% & 85% SOC) you would need approximately 900Ah's of lead to equal the 400Ah LFP bank.
You DO NOT need as large an LFP bank as you do LA so you can't honestly compare 400Ah of Li to 400Ah of lead on price / Ah's as this is a grossly unrealistic comparison.. Interestingly 900Ah's of lead, using 6V golf car batteries, weighs approx 528 pounds and 400Ah of LFP weighs 130 pounds.
#9 LEARNING CURVE / HUMANS:
By far the biggest con for LFP is relearning the human behavior developed on lead acid. Voltage for SOC is pretty much meaningless with LFP so don't bother. You don't want to float LFP, unlearn float. Get out of the habit of "charging to "full", not necessary. Stop worrying about not being able to start your motor. Enjoy the piece and quiet and even at 80% DOD the LFP bank will laugh at the starter motor current. Starting a motor at 80% DOD for LFP is like Mike Tyson picking up a feather........ Unlearn your lead acid learning's and the transition to LFP will go much more smoothly. Human behavior learned from lead is IMHO one of the biggest cons for LFP..
#10 ADDED COMPLEXITY:
In today's day and age we live in a complex world, we always want to be within reach of internet, have multiple devices plugged in, marine electronics have become more complex and the entire boat is moving in a complex direction. LFP is going to add even more complexities to the boat. In a way it is more complex, with all the protection systems in place so as not to destroy the cells, but in another way, it is pretty simple.
How simple? Charge to full and stop... Run the bank down to 80% DOD and recharge. Repeat 2000 +/- times.... If you want a simple system then LFP is not going to be the direction for you. Perhaps the Pardey's do have it all figured out... (wink)
#11 SHELF LIFE:
There is a lot of evidence out there that suggests these cells can easily cycle to 2000 or more cycles yet there is little information about prismatic cell shelf life. LFP does lose capacity, even when not used, but how much is still open for debate. The yellow 400Ah cells in this article are 2009 cells and as of December of 2014 still delivered 419.2 Ah's under a 30A constant load at cycle 550. Of course this is an n=1, which in science means squat. These cells have never been stored at a high SOC nor in temps exceeding 80F so for LFP shelf life they have really had ideal conditions. Based on the scientific data we do have shelf life does appear to be affected more dramatically at temps above 80F and in this regard LFP is not much different than lead acid. I guess no battery really likes heat. The bottom line is to keep them stored at cooler temps and do not store them at more than 50-60% SOC. High storage state of charge, and high temps during storage, can accelerate LFP shelf life degradation. It is possible, under the right circumstances, that a boat owner may never get the claimed cycles without shelf life eating away at the capacity too..
PHOTO: In this photo I have constructed my cell compression case. LFP banks used cell compression cases so that in an overcharge event the cell bulging may be controlled. I chose 1/4" aluminum as it is easy to work with. The cover is 3/8" Polycarbonate.