You can use torque with OBD2 and load the PID for Kia Phev (https://github.com/JejuSoul/OBD-PIDs-for-HKMC-EVs) and setup the dash to monitor each cells from 1-96 for voltage.No doubt that what you are seeing is real but I don't understand how you can even see individual cell voltage. Isn't the traction battery hundreds of cells wired in series?
I been using SoulEVSpy with OBD2 instead as it has all the 96 cells setup to be displayed, you can see each individual cell voltage and Temperature per module.
The resolution I'm getting is down to 0.01 V, so you would see a change from 4.15 to 4.14.I think perhaps you are misinterpreting the numbers. It’s also an open question in my mind if it’s safe to extrapolate the numbers for the 2017 HEV to your 2020 PHEV, but let’s assume that it is (aside from the battery size, which we know is larger in the PHEV).
I assume you’re getting the 4.15 from an OBD reader? What is the resolution of the numbers it reports? Do you ever see something like 4.14, or does it go from 4.15 to 4.10? If the resolution is 0.05 V then we might contemplate that even if the actual voltage is 4.199, your reader might report 4.15. In other words, perhaps your system is charging to 4.2, and the difference between 4.15 and 4.2 is not “the buffer”.
It’s appealing to think that the cells might have been designed to have a maximum capacity of 5.0 V. If that is true, the difference between 4.2 and 5.0, expressed as a percentage of 5.0, is 16%. That lines up nicely with your observation that on the low end, the hybrid kicks in when the SOC is 16%.
On the other hand, the page you referenced points out that a 64 cell battery has 240 V at 55% SOC. That implies that each cell would have a max capacity of 6.8 V, in which case the buffer between 4.2 and 6.8 works out to about 38%.
I believe the maximum capacity per cell is 4.2 V, it is the same for HEV and PHEV.
Obviously to prolong battery life they never fully charge the cell to 4.2 V, so that's why i see only 4.15 V when charged to 100% shown on the dash in the car.
The HEV has 64 cells vs 96 cells for the PHEV.
The max voltage per cell 4.2 V was from the Kniro tech site which is for the HEV.
Operating Voltage (V)
160 - 275
[2.5V ≤ Cell Voltage ≤ 4.2V]
For the PHEV when fully charged to 100% the battery voltage was at 398.4 V / 96 cells = 4.15 V per Cell.
This was all observed using OBD2 connected to SoulEVSpy and confirmed using torque with PID for the Niro PHEV