Yes, it changes the OTC values significantly. You’ll need to recalibrate the OTC values and voltage values completely. The tools for this are under ToyKeeper/battcheck/offtime-cap.hex and battcheck.hex.
Voltage is relatively straightforward; connect it to a power source with the voltage you want to measure, read the blinks, put that value into your target firmware. Repeat for each voltage level you need to measure.
Offtime is a bit harder, unless you have a robot to press connect/disconnect power with very precise timing. Basically, connect power, disconnect it, wait for the time you want to measure, connect power again. Repeat a bunch of times to get an average, and use that.
If you keep getting 255, it means the time is out of the MCU’s measurement range (too short), or a 0 means it’s too long. The problem I get is that it stays at 255 for a while before the OTC voltage drops into the usable range (especially when the light is cold).
Ideally, you want both voltage and OTC values to be near the middle of the measurement range for the best accuracy and consistency. The values should ideally center around 128 or so, though really anything between 64 and 192 is good. Probably anything between 32 and 224, really. Outside of that though, it’s getting into the range where it’s hard to measure reliably. The only way I know to adjust this is by choosing different resistors.