Would be interesting to know whats going on in the industry with LFP. Pre-built lead acid replacement LFP battery prices have been dropping almost daily and are down to high end AGM prices [1] and quality has been going up [2], these batteries were twice the price a year ago.
Will be replacing the lead acid in my RV soon with LFP's, it really a no brainer.
Can you help me understand why you wouldn't just stay with the old Lead-Acid batteries? You can get a 150Ah for $110, for example, whereas this 100Ah you linked to is $376.
I'm sure there are benefits, but I don't know much about batteries to understand why you'd make that tradeoff.
You can't discharge lead-acid as deeply as LFP without destroying longevity. So that 150Ah, probably only has 75Ah of useable capacity.
The LFP battery will also last for ~5000 cycles, after which it'll still have ~80% capacity, and thus is still valuable. Lead acid only has a life of 500~1200 cycles. In other words: you'll have replaced the lead acid battery 4~10 times before you need to replace the LFP.
IIRC, lead acid has a higher voltage drop when drawing a lot of current. Meaning that with LFP you can power larger loads.
Taken together, for most use-cases, the lifetime TCO of LFP is better than lead acid.
> The LFP battery will also last for ~5000 cycles, after which it'll still have ~80% capacity, and thus is still valuable. Lead acid only has a life of 500~1200 cycles. In other words: you'll have replaced the lead acid battery 4~10 times before you need to replace the LFP.
What happens if you keep using the LFP battery after that? Does the capacity continue to fall to zero, or is there some point it levels off and you can use it indefinitely after that if you don't mind the reduced capacity?
The curve seems to be pretty lineair. So I think you can do another 5k cycles and have 60% left, once more for 40% etc. A quick search didn’t reveal a full curve chart to zero though. I know that a lot of cheaper LFP cells on aliexpress are used “grade B” cells, eg cells that had an original capacity of 120Ah that are resold as 90Ah cells after their first 5k cycles.
Peukerts law does not really apply to lithiums [1] so with lead acid your capacity is greatly reduced if you do high amp draws.
You can really only use 50% of lead acid capacity without significantly effecting their lifetime, so most people cut the capacity in half when discussing, lithium can be run to 80% without issue and really even 100% with minimal loss and LFP's have much greater cycle than lead anyway so you probably pay less in the long run with a LFP than buying multiple lead.
LFP hold their voltage pretty consistently right up to the end of the discharge cycle while lead acid will drop significantly, this increases amp draw and has other negative effects (dimming light etc). The low internal resistance makes them pretty stiff voltage sources.
LFP accept bulk charge much longer before hitting absorb than lead so they can be charged much faster, this helps when charging from a generator as you don't have to run it as long to get full charge. Also you don't really have to worry about partial charging, where as with lead you want to do a full absorb regularly to keep their capacity up.
At least half the wieght.
Top tier lead AGM like Lifelines are basically the same price, I have these in my RV now and are a out 7 years old and now need to be replaced due to not holding a charge. Lifelines are considered gold standard and have high charge and discharge capability for lead acid, but LFP still blow them away, so no reason to go that route again.
Those cheap lead acids are not going to be decent deep cycle and will be wet cells, so will have off gassing and cause corrosion. AGM solve that and good deep cycle AGM's are not cheap, see Lifeline, Trojan etc. You can get relatively cheep "golf cart" batteries but again wet cells that need water checked and have to vented properly.
There are downsides to LFP:
More complicated, they need a BMS to protect from over and under charge, the BMS has current limits due to using FETs to switch on/off, so most of the drop in replacements can only do 100 amp continuous with short burst of say 300 amps. So they are not great engine starting batteries. You can run in parallel to get more current capacity obviously. BMS is a full microcontroller with high current disconnect so much more to go wrong, although some have bluetooth with an app to monitor individual cells etc.
They can't be charged below freezing without damage, so most BMS have low temp disconnect to protect against that. Also there overall temp range is narrower than good lead acid, my lifeline are rated -40f to 160f I believe. Lead acid are simple tough and reliable.
Last I heard, LFP had some significant temperature restrictions compared to lead acid, making them unsuitable for use in cold temperatures. Has that changed?
Will be replacing the lead acid in my RV soon with LFP's, it really a no brainer.
1. https://www.amazon.com/dp/B08FMTRYPT
2. https://www.youtube.com/watch?v=xBonGQe363g