No article would be complete without pro's & cons and comparisons between lead and LFP.
*CYCLE LIFE: 2000+ "claimed" cycles to 80% DOD (depth of discharge). If we compare the best AGM batteries to LFP we find that reputable manufactures such as Enersys/Odyssey claim just 400 *lab rated cycles to 80% DOD.
I suspect, (wild ass guess), that LFP prismatic cells, from reputable manufacturers such as Winston, CALB, Sinopoly, Hi Power, GBS and others, can last approx 1600-2400 cycles even when pushed regularly to 80% DOD, in the real world of the marine environment. The manufacturers claim more, but so do the lead acid makers, and these are always ideal "lab" conditions. Of course at this point in time this is a WAG (wild ass guess) on my part. I can assure you even 1600+ cycles is a very long time. I have been busting my hump for approx 28 months and have only managed to put 550 cycles on this bank and that is with accelerated cycle testing..
Of course the average lead acid battery on boats is often dead well before 150 cycles and they rarely if ever even come close to the "lab rated" cycles. Do the math on your own bank, be honest about it, and see how many cycles you had, to 50% SOC, before your bank needed replacement. Most boat owners are shocked when they do this math.
*I have never seen a single lead acid battery bank hit its lab rating in the marine environment, especially not on cruising boats. These lab numbers are fairy-tale ratings when translated into the real world. I also don't entirely trust the lab ratings of the LFP cells, though some have done the testing and have seen this.
Alex MeVay the CEO of Genasun firmly believes in 2000+ cycles to 70% DOD. This is utterly amazing cycle life if it can really happen. Based on what I am seeing at 550+/- cycles I am trending towards believing it..
*USABLE CAPACITY RANGE: Approx 80% of an LFP banks capacity is fully usable. With lead acid you often have just 30-35% usable capacity (50% SOC to 80-85% SOC) due to charge acceptance current limiting. With LFP current limiting or acceptance taper is very, very short in duration, even at relatively low charging voltages of 13.8V - 14.0V.
*CHARGING SPEED: Very, very short current taper even with large current sources. Charge to nearly full before even attaining absorption voltage. This of course is entirely dependent on your charging voltage and your current source. We charge at 120A steady (160A alt set up to run at 120A continuously) and our current taper lasts only 30-35 minutes. Compare that to HOURS and HOURS of current limiting using a 120A charge source on 400Ah lead acid batteries. With a small charge source, like solar or wind, you will hit 99%+ SOC before any current limiting occurs. Our bank literally has to be chock full before our solar array can even get to 13.8V.... These batteries can take immense current, and charge extremely fast, but really tend to do extremely well with .3C to .5C in charge current.....
*WEIGHT/SPACE: Less than half the weight of lead Ah to Ah and almost always more compact. The 400Ah bank in this article weighs 134 pounds less than a 400Ah lead acid bank. However, to equal the usable capacity of a 400Ah LFP bank you would need approx 900Ah's of lead. This makes the 400Ah LFP bank approx 400 pounds lighter than the equivalent usable capacity in lead acid!
*GET OUT THE DEAD LEAD: The term "dead lead" is s term I coined in my electrical seminars. The typical lead acid bank consists of 65-70% of the weight being comprised of "dead lead" or the excess lead you carry around but that you can not use. If you have a usable capacity of just 30-35% of the bank, when out cruising, this means that you are carrying around 65-70% of that weight in unusable "dead lead" capacity. This 400Ah LFP bank weighs 130 pounds & 80% of it is easily usable. This means just 20% of it not easily usable or you simply don't want to use it for best longevity. As a result, we carry around a measly 26 pounds of unusable battery on our 36 footer..
Lets go back to usable capacity for a moment. If we want to equal the usable capacity of this 400Ah LFP bank in lead, we would need 8 GC2 6V golf cart batteries or approx 900Ah's. 35% of 900Ah is a usable capacity of 315Ah's. 80% of the 400Ah LFP bank is a usable capacity or 320 Ah's. The 900Ah lead bank weighs 520 pounds. If you use just 35% of that bank then you are hauling around 338 pounds of "dead lead" or 338 pounds of unusable capacity.. Twenty six pounds of unused LFP or 338 pounds of "dead lead"..?? Points to ponder...
*STEADY VOLTAGE: LFP banks have a very strong & flat charge & discharge curve with a very steep & fast rise or drop at either end. These ends are called the "knee's". LFP's will maintain voltages well above that of any fully charged lead acid bank, and remain very close to their 3.3VPC / 13.2V nominal voltage level, and hold quite steady voltages with little change almost all the way to 80% DOD. They will maintain a very tight voltage range even under "normal" house loads. Espar heaters, refrigeration, watermakers etc. will all perform better. Equipment likes higher voltages. Even bilge pumps will pump more water. Voltage sag that can drop out electronics during bow thruster or windlass use is almost entirely eliminated.
*CHARGING EFFICIENCY: Charge efficiency is also referred to as the Coulombic efficiency. These batteries are as near 100% efficient as I have ever seen on my test bench. Take 200Ah's out and put 200 Ah's back in and you hit the voltage and net accepted current at almost the exact same Ah's out to Ah's in. Until LFP I had never witnessed anything like this, even with the best AGM's. Lead acid ranges from 70% to as high as 90% +/- efficient but you still need to put back in 10-30% more than you took out, and this is with "healthy" lead acid batteries. As they sulfate the charge efficiency or Coulombic efficiency gets even worse.
*NO NEED TO RECHARGE TO 100% SOC: We know the Achilles heel of lead is sulfation and in order to fight off sulfation we need to charge them to 100% SOC as often as possible. This proves very difficult for many boaters and cruisers unless your boat resides at a dock after each sail or sits on a mooring with an adequate solar system. LFP batteries do not need to get back to 100% SOC so, FOGEDABOUTIT.......! This is a major win for LFP. When we come back from a weekend on the water, and our battery is at 50% SOC, I DON'T CARE!!!! I shut down the boat, and the solar and go home. LFP batteries actually prefer to sit at 50-60% SOC rather than at 90-100%.. As I said earlier this is a mental paradigm shift we need to overcome in our human behavior/thinking around our batteries...
* SULFATION, WHAT'S THAT?: Sulfation is by far and away the cancer and #1 killer of lead acid batteries. These batteries do not sulfate, no cancer, so there is no need or worry to constantly get back to 100% SOC before you leave your boat. LFP batteries actually prefer to be left at mid range SOC rather than full. Enjoy that sail home, WITHOUT THE MOTOR!!!
*SAFE Li TECHNOLOGY: Without question LFP is currently one of, if not the, safest of the Li battery formats. Many argue, and these arguments have certainly been well made, LiFePO4 is as safe or safer than lead acid.
FACT: Lithium Iron Phosphate cells/batteries can enter thermal runaway and catch fire. Once on fire these fires are very difficult to stop. While it's much more difficult to cause thermal runaway in LFP it's not impossible.
ALL BATTERIES ARE DANGEROUS!!
Let us not forget that. As Li goes LiFePO4 is currently the safest widely available option. Remember we are surrounded every day by far more volatile Li technologies in computers, iPads, iPods, tablets, video games, cell phones and even cordless tools. LFP is less energy dense than other more volatile Li formats, but when compared to lead acid everything looks energy dense. We have no need on boats for "Dreamliner" level energy density, thus the vast majority of marine systems use LiFePO4/LFP technology not LiCoO2 like Boeing chose.. If you believe LiCoO2 & LiFePO4 batteries are the same PLEASE STOP READING HERE and go back & hug your lead acid batteries.....(grin)
I think this video done by Sinopoly can sum up the safety of LFP technology. Those crazy Chinese guys shot, burned, shorted and cooked these cells. Please DO NOT attempt this stuff at home. Take note that a single 60Ah 3.2V cell can throw in excess of 1800A of current into a dead short.. WOW! None of the testers got acid burns, were blinded or went home with holes in their clothes. (wink)..