question

First, people get really hung up on cycle life. LFP battery cycle life is so high, calendar aging is likely to be a bigger influence on their life than cycling. Regardless of use, there will be notable deterioration in 5-10 years.

Please cite these studies. I've heard the same and accept it, but I've never seen hard data to back it up. It is also MORE true for non-LFP battery chemistries like NCA, NMC, LMO or LiPo.

An issue with LFP is it has a terrible voltage to SoC relationship in an active system. Floating on a voltage basis, which is how all chargers work, will actually continue to charge taking the battery above the target 80% SoC.

Per Victron, the Smartshunt needs to be synced at 100% SoC 2+ times per month to maintain accuracy, so failing to fully charge your battery regularly will cause the shunt to lose accuracy.

Additionally, LFP batteries that are only charged to 80% are very likely to go out of balance due to the cell voltages never reaching the balancing threshold. This can result in temporary loss of usable capacity. There are cases where battleborns have lost almost 50% of their suable capacity because they were never operated at the higher voltages that allowed balancing.

It is known that charging is stressful. By reducing the charge voltage and subsequently the current, LFP cycle life can be improved. The downside is that the charge time is more like lead-acid.

Absorption voltage at 3.45V/cell with a tail current of 0.02C will get you > 98% SoC and reduce charging stresses.

Float should be 3.35-3.37V/cell.

None of the equipment you are using has the means of targeting 80%. If you had a BMV-712, you could use the relay to turn the MPPT/Multiplus charger off when the battery hit 80% then turn it back on at some lower SoC, but the smartshunt lacks this feature.

If you just need to feel better, set the absorption/float/tail current as I described.

Otherwise, use the manufacturer's recommended settings.

Both should results in thousands of trouble free cycles and likely several years of use.

@snoobler ... you've wrote ...

"Absorption voltage at 3.45V/cell with a tail current of 0.02C will get you > 98% SoC and reduce charging stresses" ...

My questions ...

A tail current of 0.02C ? What will it give by a 160Ah LiFePo4 battery ?

What is your advice for Absorption-time setting in this matter ?

Many thanks

0.02 * 160A = 3.2A

Absorption should be FIXED and set long enough to allow it to reach the tail current.

Very easy to implement with solar.

This can notably increase AC charging time. On shore, it's not a big deal, but on generator, it's not particularly desirable to extended run times.

You likely need to experiment with your charging methods to see what works. If charging from generator, probably best to set absorption at 14.2-14.4V with the absorption time set to no more than 30 minutes.

If charging from shore, I don't believe you can set a tail current. Start with fixed absorption time of 4 hours and see how long it takes to get to 3.2A.

It may also be easier to target a window of tail current. 3.2-8A charge termination criteria should still get you well north of 90% charged and reduce charging stresses overall.

@snoobler Thanks a lot

Here's an example 30%SOC 10 months at 104F capacity loss 5%, 60% SOC then 7%, 100% SOC then 10% but at 122F and at 100% SOC the capacity loss is 25% in ten months. References below.

The real evidence: Who isn't selling batteries and is responsible if they fail early. Oh, my new car. I have 30,000miles on a 22 Chrysler PHEV Pacifica with 18 kwhrs of LFP batteries apparently from the LG plant in Michigan. I naively thought the 18 number was the usable capacity and the indicator on my dash went from 0 to 100% and I only got 2 mi/kwhr unlike sedans that get 3. However looking at my Emporia wall charger history, every full charge was 12.2 kwhrs. So that is 2/3 so maybe my Pacifica is running the batteries from maybe from 15% to 81%. My VanCamper system is newly installed and I don't even have my regular settings all correct, but it really looks like Victron only wants me to use 28.4 and 27.0. I understand the balancing but why not let us set this float 27.0 at something lower? At the moment I have tried typing in several places a lower voltage but I think my Lynx BMS is smarter than me and won't let me.

2022 review paper. https://doi.org/10.1016/j.esci.2022.03.006

Insights for understanding multiscale degradation of LiFePO4 cathodes

Li Wang a, Jingyi Qiu b, Xiaodan Wang a, Long Chen b, Gaoping Cao b, Jianlong Wang a,

Hao Zhang b,*, Xiangming He a,*

a Institute of Nuclear and New Energy Technology, Tsinghua

Some of the data from Journal of The Electrochemical Society, 163 (9) A1872-A1880 (2016)

Calendar Aging of Lithium-Ion Batteries

I. Impact of the Graphite Anode on Capacity Fade

Peter Keil,a,∗,z Simon F. Schuster,a J¨orn Wilhelm,a,∗ Julian Travi,a Andreas Hauser,b

Ralph C. Karl,a and Andreas Jossena,b