It appears that my previous post disappeared......for some unknown reason.
Even when "OFF" there will be some electronics active, just to detect things like when you turn it ON.
When it is running on propane, there is a solenoid valve held open to allow the gas to flow....and some other stuff too probably.
I too think this is perfectly normal.....and even if not it is not a significant factor in your short battery life.
P.S. when completely disconnected the current flow is ZERO......indicating a slight fault in your meter or technique if it show anything above zero.