I don't think I've actually told you where I relocated the 12V aux battery in our C-Zero. I did put the fuel burning heater where the 12V lead acid battery usually is. From there, and the positive battery terminal, I ran a 16 mm2 red cable into the cabin thru the grommet below the center console and under the back seat. I took out the styrofoam box containing the tyre fixing equipment and put a 12V 20Ah LiFePO4 battery there. It has a 100 A fuse on it, which is plenty
The battery in question is one of these:
It's been functioning perfectly so far. It usually sits at 13.3 V when the temperature is normal, a little less when frozen. The car keeps the 12V bus at about 14.5 volts when it's running or charging. That's about 3.6 V per cell, which is quite ok. The cells are as they came, I didn't do a bottom balance on them myself. I think they ship these 12V batteries with balanced cells.