williamwright formulated on Sunday :
What appears to be leakage from the vehicle battery is just meter error I
think.

If it is a modern vehicle, it will have various circuits which need
some small amount of power to maintain its systems. My cars various
computer systems, once fully into sleep mode, draw around 20mA. Even
that 20mA pulse higher, when the alarm system has a 'quick look
around'. Only older cars had no discharge at all, when parked, unless
they had alarm systems.