Some advice for your visit to the dealer:
Others have reported that dealers tend to dismiss any values not read by the KDU (KIA Diagnostic Unit). Some dealers either believe they can improve the GoM by applying BMS updates, or know that applying the updates results in the BMS using default values and needing several cycles before valid data is available. When they do that, they will get a value well over 70%, and send you on your way.
Make a copy of
PS 548 and request they carry out the procedure in it exactly as laid down, explaining that you are well aware that applying updates prior to reading the BMS data will prevent a correct SOH reading. Highlight the relevant words on the copy and draw attention to the highlighted text.
Provided the reading is less than 70%, that should result in a dealer report to KIA Corporate and, in turn, a replacement battery.
Also, you can calculate your SOH:
After charging, reset the m/kWh (shows "--" when reset). Note the mileage and the battery %age if not 100%. At the next charge note the mileage and the battery %age before charging commences and note the m/kWh. Divide the difference in mileages by the m/kWh to get the kWh consumed. Divide this by (difference in %ages x 0.01, i.e. a decimal fraction). This gives the kWh capacity at 100% charge. Divide that by 27. 30, 39.2, 64 or other value, depending on the nominal battery size, and multiply by 100 to get SOH.
I have tested the method against Spy, and it gives close agreement.