Testing has shown that the Range Device has a very small battery draw when the vehicle is off and in "sleep" mode. This is because it needs a monitor running to catch when the vehicle is started. This small draw is not enough to adversely affect battery life or drain the battery unless left in place for an extended period of time (i.e. more than a week or two).
Our testing has shown that in the normal vehicle, it shouldn't affect vehicle starting for several weeks HOWEVER very cold or very hot weather can drastically reduce battery capacity, as well as any other accessories or modules in the vehicle that stay "awake" with the key off. Many security systems, aftermarket radios, plug in phone chargers and so on may also have a slight drain when not in use, so best practice is to unplug the MDS Manager when you know the vehicle is going to be sitting without starting or driving for several days.
To add some more detail:
The device will go to a VERY low "sleep" state after the engine is off (within 3-10 seconds of the engine shutting off)
In this state all the LEDs are OFF and it hibernates at about 1-3mA
Every 7-25 seconds it will wake up to a "light sleep" state to check to see if the vehicle is running. In this mode, there will still be NO LEDS lit but current draw will spike for < 0.1 sec to about 7-10mA.
If the vehicle is NOT running (i.e. RPM < 500) then it'll go back to deep sleep. Rinse and repeat until the vehicle is running, at which time it'll fire up completely and you'll start seeing LEDs light again.
Given this and the normal draw from other modules (a modern vehicle will always have a small draw for the security systems, BCM, remote start/locks, OnStar, etc. .. sometimes as much a 50mA), it is recommended to reduce the risk of battery depletion by unplugging the module when the vehicle is going to be sitting for an extended period. Cold weather, weak charge state, age, etc. can all contribute to less battery capacity.
A healthy battery with decent capacity should be able to go much longer than the recommended length of time but it worth it not to come out from a 3 week vacation and find the battery dead in the airport parking lot!