Running a generator to exercise it when there's shore power?

our home 20 kw back up propane genny auto start exercises once a month. for a few minutes.its battery is maintained, from the home power. Fuel is not the issue, no water or contaminate can enter into propane, as could happen with water condensation in gas or diesel tanks.
engines , derive their power from an fueled internal power source. in definition from motors whiich are powered by an external power source, such as electrically, should be exersized occasionailly to maintain them when you need them