It's easier to replace the pack as I don't believe any dealership in the UK has the training to replace individual cells yet. Even nissan only have 2.340 mile weekly round trip? Cripes. You must have the patience of a saint
Hope Kia do the sensible thing and replace enough of the battery so that it's not just sitting at 71% SOH afterwards
It's sounds like your weekly cycle is doing a good job of killing off that weak cell and the BMS is seeing that now as it's pulling the whole pack down with it as it's triggering the low voltage thresholds earlier than the others. Would be interesting to see a leafspy style version which shows each cell and if it charges quicker than the others as well and thus your not even getting near full as it's getting there first and draining first as it's starting to fail.It's dropped to 60.4% this evening...just sitting there.