Is this SoH OK?

[MickeySw]

However, any reported SOH will need to be taken with a pinch of salt because, for EV applications, manufacturers build in a hidden "upper" buffer of unusable capacity. Hence any significant degradation in SOH can be mitigated by the EV's BMS software 'releasing' some of that buffer in to general usage so as to reduce the apparent degradation of SOH to the average user. So, without knowledge of the amount of upper buffer that has been deployed, the SOH is somewhat meaningless.

EV manufacturers deliberately underreport the max capacity of a HV battery by a few %, therefore SoH will remain 100% until that ‘buffer’ is ‘used up’.

I agree, a SoH of 100% is somewhat ‘meaningless’, however once you drop below 100%, SoH will become accurate.

Imho the only way for the BMS to release ‘unusable hidden upper buffer’ for ‘general use’ is to increase the cell voltage, has anyone seen evidence of that happening?

 

[Everest]

OK, I didn't mean increase the SOC to which the battery is charged, I meant a release of top buffer to keep the apparent SOH higher. From what I have read about on the Internet (so it must be true!!) some manufacturers, e.g. Tesla and VW for example, have algorithms to make some of that under-reported capacity available. I suspect that would be done over time, rather than all at the beginning - but who knows

 

[MickeySw]

OK, I didn't mean increase the SOC to which the battery is charged,

The battery is always charged to 100% SoC, however the actual capacity is a bit higher than the spec but all calculations, (range, SoH) are done using the nominal (lower) value.

Once the degradation has ‘used up’ the ‘overcapacity’ SoH will start dropping.
There is some ‘anecdotal evidence’ as handful of preFL SR MG5s still show 100% SoH after years of (ab) use, it’s thought they were actually equipped with ‘reject’ LR battery packs??

I meant a release of top buffer to keep the apparent SOH higher.

The top (and bottom) buffers are created by limiting the voltage range the BMS will use (e.g. 3V-4.2V) when the cells themselves are capable of more (e.g. 2.8 - 4.3V).

Increasing the top ‘cut off voltage’ will add more capacity but it’s also thought to increase degradation, not sure if there is any net gain?

 

[Data]

OK, I didn't mean increase the SOC to which the battery is charged, I meant a release of top buffer to keep the apparent SOH higher. From what I have read about on the Internet (so it must be true!!) some manufacturers, e.g. Tesla and VW for example, have algorithms to make some of that under-reported capacity available. I suspect that would be done over time, rather than all at the beginning - but who knows

All manufacturers make the upper & lower buffers available to the BMS. This normally happens only during the equalisation/balance charge. That is where all battery cells are balanced with, in effect, excess energy above 100%. This buffer must also be accessed to prevent premature degradation of the buffer. That's why doing these 'proper equalisations' is so important. Running for long periods with unevenly balanced cells reduces battery capacity (as you mention) & reduces state of health of the battery as the BMS will recognise the reduced capacity which after a short while becomes permanent.