Do I NEED to fill up every so often?

Sorry; your missing the whole point of this thread. Driving the car for 3 minutes is HV mode is even WORSE than staying in EV mode. Those short hops is dumping raw fuel and contaminating your engine oil even more. The motor needs to run long enough and hot enough to burn those contaminates out. Fuel will migrate out of the oil at relatively low temperatures, but moisture will require higher temperatures for a longer periods to be released from your motor oil. It's not just running the motor, just to run the motor - it needs to heat-up and burn out contaminates that accumulates in the motor oil. Moisture in the motor oil will encourage internal corrosion. Gasoline in motor oil will strip the adhesion properties of the motor oil to the smooth machined surfaces that it's suppose to protect. Lastly; it'll be hard on your CAT, since it needs to get up to a certain temperature to operate properly.

Hope this helps.....

 

What’s the rough door-to-door distance of the 3 minute drive? Speculating, considering average speed of 30 mph:

3/60 x 30 = 1.5 (miles).

^ Interesting, when I typed the above (in Safari on iPhone), it auto-completed the 1.5.