SoC suddenly dropping 3%

[girarcat]

Hi,

When driving to work, I leave home at 80% SoC. I drive for 60 miles on the motorway and get to my workplace with around 53% of remaining battery. Several hours later, I get back to my car to drive home, where I arrive with a SoC of about 20%.
However, as of late, quite often when I get into the car at my workplace in order to drive back home, in less than 1 mile the SoC drops from 53% to 50%, and I've only driven around the parking lot + joined the main road (notice that when getting into the car, SoC is exactly the same as when I left it several hours before). Then normal battery consumption rate is resumed (and this only happens every now and then, many other days there is no such sudden drop). Temperatures are around 20ºC, so I assume neither heating nor air conditioning could have a significant impact.

Why do you think this is happening? It sort of annoys me because when this happens, it means that I will reach home below 20%, which is what I normally try to avoid. To me it kinda looks like some SoC indicator calibration issue, more than an actual drop in terms of remaining battery...

Thanks

[Chequers]

When was the last time you did a balance charge ?

[mluisbrown]

I've had the opposite happen. Driven a long journey, from 100% down to 6%, then charged to 30% whilst having dinner and after dinner it's jumped from 30 to 37% I've had a similar jump occur again after a similarly long drive using almost all the battery. It must just be the battery management system recalibrating the SoC indicator.

[girarcat]

When was the last time you did a balance charge ?

hi, thanks for your answer. What is exactly a balance charge?

[girarcat]

I've had the opposite happen. Driven a long journey, from 100% down to 6%, then charged to 30% whilst having dinner and after dinner it's jumped from 30 to 37% I've had a similar jump occur again after a similarly long drive using almost all the battery. It must just be the battery management system recalibrating the SoC indicator.

Sometimes, when leaving home at 80% SoC after charging the car, within the first mile it will jump up to 82%.

[Ponk]

When was the last time you did a balance charge ?

hi, thanks for your answer. What is exactly a balance charge?

Charging to 100% every so often to “balance” all the cells. But I also read that slow charging to around 80% at home does this, but I am really not sure, it’s not something I bother about.

Everybody probably experiences what you see, a quick drop of a few % and sometimes and increase of a few %.

I would not any of these thing bother you, the range etc all averages out over the journey.

[girarcat]

When was the last time you did a balance charge ?

hi, thanks for your answer. What is exactly a balance charge?

Charging to 100% every so often to “balance” all the cells. But I also read that slow charging to around 80% at home does this, but I am really not sure, it’s not something I bother about.

Everybody probably experiences what you see, a quick drop of a few % and sometimes and increase of a few %.

I would not any of these thing bother you, the range etc all averages out over the journey.

In that case, yeah, every now and then I top up the battery to 100%, and the issue persists.

[DrEVil2024]

Every once in a while, I charge to 100% (and then use it within 10 hrs) using my 13A charger lead.

If I am going to my mums house, which is about once every few months, then I charge to 100% with the 7KW charger and use it almost immediately.
When I get to her house, I use the 13A charger to top it back to 100% to get home again.

That is the only 100% charging mine gets. But, the battery seems to be behaving.

I do find however that a charge to 80% using the slower 13A trickle charge lasts longer than the 7kw charger. I can go a fair distance before the 80% starts to drop when you use the 13A lead.
The range drops almost immediately I drive off when I use the 7kw charger.

[girarcat]

Hi,
I've been testing the issue a little bit more. Now it seems to happen every single time I reach my workplace at a SoC near 50%.
When taking the car back home after being parked for the day, I always experience this drop of 3-4% within the first mile. Then battery usage stabilizes.
What's weird is that those days I decide to charge the car up to 90 or 100% (and thus I reach my workplace at around 60 or 70% SoC instead of 50%) there is no issue whatsoever. There is no sudden drop in the SoC when I drive back home (also, while driving back home and SoC decreases across 50%, it decreases steadily without weird drops).


There is also another weird thing that might be related to this. If when reaching my workplace I have a look at the average consumption for that trip shown on the car's display and manually convert that into % of battery (considering a full battery to be 77kwh), then the numbers I get make total sense and are coincident with what the car shows (meaning that if the average consumption for that trip has been 0.21kwh/km and I've driven 100km, I have used up 21kwh, which is a 27% of 77kwh, so my SoC at that point should be around 53%, which is exactly what the car is showing, so no issue here).
However, If I do that same calculation when arriving back home, according to my numbers the SoC at that moment should be around 25%, however the SoC shown by the car is way lower, about 18%. So it seems that around a 7% of battery has disappeared somehow.

Do you think all this could be related to some battery cell being damaged/degraded or maybe just some calibration issues?
I think we could summarize all this by stating that whenever SoC is above 50%, all numbers add up. When SoC is below 50%, some funny things start to happen.

[A4d]

My trip to work takes 9% and the return home is about 11%, either it’s more down hill on the way work than the drive home or I am more keen to get home a drive faster.