Peter WA
Established Member
I've got a theory that I would like to test.
The theory is: in the Mk2 ZS EV with LFP battery (standard range), the battery State of Health (SOH) reported by the car is a fudge, that is nothing other than a count-down timer, that started running when the battery pack was manufactured, and decreases linearly with time.
That countdown is calibrated to ensure that it will remain over 70% for the duration of the 7-year warranty period. The decrease in reported SOH is set to about 3.8% per year, which over 7 years would equate to 26.6%. Or 0.0104% per day.
Here is a chart of my car's SOH since I got OVMS working for it, about 1 week after I got the car. The only bumps are when the data wasn't updated for a few days. Feel free to hold a ruler against the bottom of the line to see how straight it is.
So far I've only got data for 2 cars. My own and one other. For my car: production date of the car is known, according to contract information: 28/8/2022. If I extend the chart back into the past, it will reach 100% on 18/8/2022 - quite reasonable to have the battery pack assembled 10 days before the vehicle left the factory.
It would be great if some people here can confirm (or refute) that theory. Please post SOH and production date as replies. Only Mk2 ZS EV with LFP battery please (standard range). Or alternatively, if you don't know production date, read out SOH a few days apart, and check whether the daily decline is in line with what I predict.
Of course I've got an explanation. I believe MG engineers found it too hard to measure SOH. And a meeting took place a bit like this (all facts above, pure fiction below):
Product manager: Did you finally manage to measure SOH for the new LFP batteries?
Engineer: Sorry, we can't figure out how. The voltage curve is just too flat. Maybe we'll have some great idea later, or it will become easier to measure once there's significant degradation.
Product manager: But the cars will enter production next month, and SOH is part of the warranty conditions. We need to populate that PID.
Engineer: How about we just set it to 100% and once we've figured out how to measure, we'll apply a software update?
Product manager: No one will believe it stays at 100%, if we do that, at the first service people will find out something isn't quite right.
Engineer: How about a linear decrease over time then?
Product manager: Sounds like a plan, just make sure it stays above the warranty cut-off. And make sure you keep working on it, so we can do that software update to fix it.
The theory is: in the Mk2 ZS EV with LFP battery (standard range), the battery State of Health (SOH) reported by the car is a fudge, that is nothing other than a count-down timer, that started running when the battery pack was manufactured, and decreases linearly with time.
That countdown is calibrated to ensure that it will remain over 70% for the duration of the 7-year warranty period. The decrease in reported SOH is set to about 3.8% per year, which over 7 years would equate to 26.6%. Or 0.0104% per day.
Here is a chart of my car's SOH since I got OVMS working for it, about 1 week after I got the car. The only bumps are when the data wasn't updated for a few days. Feel free to hold a ruler against the bottom of the line to see how straight it is.
So far I've only got data for 2 cars. My own and one other. For my car: production date of the car is known, according to contract information: 28/8/2022. If I extend the chart back into the past, it will reach 100% on 18/8/2022 - quite reasonable to have the battery pack assembled 10 days before the vehicle left the factory.
It would be great if some people here can confirm (or refute) that theory. Please post SOH and production date as replies. Only Mk2 ZS EV with LFP battery please (standard range). Or alternatively, if you don't know production date, read out SOH a few days apart, and check whether the daily decline is in line with what I predict.
Of course I've got an explanation. I believe MG engineers found it too hard to measure SOH. And a meeting took place a bit like this (all facts above, pure fiction below):
Product manager: Did you finally manage to measure SOH for the new LFP batteries?
Engineer: Sorry, we can't figure out how. The voltage curve is just too flat. Maybe we'll have some great idea later, or it will become easier to measure once there's significant degradation.
Product manager: But the cars will enter production next month, and SOH is part of the warranty conditions. We need to populate that PID.
Engineer: How about we just set it to 100% and once we've figured out how to measure, we'll apply a software update?
Product manager: No one will believe it stays at 100%, if we do that, at the first service people will find out something isn't quite right.
Engineer: How about a linear decrease over time then?
Product manager: Sounds like a plan, just make sure it stays above the warranty cut-off. And make sure you keep working on it, so we can do that software update to fix it.
