Voltage alone does not tell you the SOC. This is a common beginner mistake when working with LiFePo4.
There are three significant parameters that affect the final SOC when charging LiFePo4 batteries:
the charge current during the CC phase
the charge voltage during the CV phase
the cutoff current
Let’s take a 100Ah LiFePo4 cell.
Case 1: Charge with 50A up to 3.65 V and cutoff when current drops below 5 A (this is the definition of 100% charged from most cell manufacturers).
Case 2: Charge with 20A up to 3.5 V and keep it in absorption for 1 hour. The cell will be charged to 99.99% of Case 1, with the same degradation.
So the apparent “limiting” imposed by the manufacturers is not real in PV systems where we have variable charge current and cannot cutoff the batteries at the end of the charge.
Looking at it another way, when our 100 Ah cell reaches 3.5V, it has a higher SOC in Case 2 than in Case 1.
If you do a little research, you will find that using higher temperatures is a scientifically accepted method to speed up processes in long-term battery cell tests. As long as you keep using the same temperatures when varying other parameters (e.g. SOC range), the results will show the impact of the other parameters (average SOC in this case).
This is a scientifically accurate peer-reviewed paper that comes to this conclusion: The average SOC was found to be the most critical factor influencing capacity fade for LFP cells
Do you have any practical suggestions to the application of this information in the context of Victron equipment or is the purpose of the information to simply reinforce the assertion of the original poster?
And also for re iteration, if the manufacturer of the battery being used says to do things a certain way, then do it. It is on them if it is incorrect.
No one needs to lose a warranty over internet articles and chat gpt.
I do know from experience/experiment a battery pack that never is allowed to balance does not do well.
I would also like to re iterate that nobody has suggested that they use the batteries in any way that does not comply with the manufacturers recommendations.
You do not need DVCC or a Cerbo or a smart BMS or a shunt to comply with manufacturers specifications on battery management.
My friend, one of the best professional offshore sailors in the world, has two Victron lithium batteries, a small BMS and a solar controller.
If someone does not wish to charge their batteries to 100% each and every time and leave them at 100% for extended periods, this is fine. It may not be advantageous, but it is not going to void a warranty. As long as the batteries are charged and blanched according to the levels and frequencies specified then all is well.
ChatGTP is simply finding and summarising all of the knowledge that humanity has acquired. It might be far more accurate than someone’s anecdotal experience and very limited experiments.
My problem is this. (And its not with chat gpt) Too many internet articles (which is chat gpt’s source) vomit out copycat information which is incorrect/unverifies or half baked. And somehow through the sheer number or repetitions it has become ‘truth’.
There is an entire community of people who take and test ideas found on the internet. As well as battery manufacturers who develop management systems for cells they have specific chemitry combination chosen. (And there are many lifepo4 vairants).
Al i am saying is be careful. I have seen warrenties being voided in the real world.
Nice article, however in real life, cells almost never stay at such high temperatures. Even if the charging rate is near 1C, which can indeed rise the cells’ temperature to 40ºC, once charging is complete, the cells’ temperature quickly lowers to ambient. Which in most cases is lower than 25ºC.
Yes, but this does not affect the conclusions.
A higher average SOC will cause more degradation even at 25 C.
The average SOC was found to be the most critical factor influencing capacity fade for LFP cells, over the factors of temperature, depth of discharge, electrolyte salt choice or graphite choice
Someone should do a study on high average SOC under lower temperatures, then. If battery chemistry was that straightforward, there wouldn’t be countless studies out there on the matter.
{these are some comments based on the study linked by mondeo man}
High temperature is a major cause of cell degrdation. So they do use it to accelerate tests. Otherwise by the time they have their results we will have experienced the same findings in our own experiences, so not useful.
They use the term (in the study linked by modeo manh edited for clarification of my following statement) soc throughout - but the use of the term (and run this through chat gpt if you like) 0% refers to under 2.55v per cell and 100% refers to 3.65v per cell. Almost no commercially programmed bms uses that range. So the battery bought off the shelf is already using the cells in studies concluded optimal range for longevity/design life
As a further thought. The electronics on the bms after 10 years would be more of a concern for me. In my experience (if the battery is treated correctly) cells can be ok, but the most replaced part is the bms as electronics fail for what ever reasons and age.
Set Peak Shaving to Always (only if you need PowerAssist below minimum SOC, there is 5% hysteresis, and the battery will be charged from the grid to the MinSOC as soon as possible).
For Kiwirob:
Limit the charging voltage in Settings → DVCC → Limit managed battery charge voltage.
For ModeoMan: There’s a right way and a wrong way to do everything and the wrong way is to keep trying to make everybody else do it the right way.
Although, if you saw someone who wants to open his wrists with the wrong side of the blade, you don’t show him the cutting edge…
