On my toad the specs said to start it every 250 miles to get the trans oil circulating.
2 years never had the battery go dead. That is until my last trip I was so close to my destination that I didn't stop for my 250 start the toad.
Well. That is how I found out that my starting it every 250 miles IS what charges the battery also.
Others will chime in what you can add on to prevent battery drain.
And check that you have the key in the correct position for towing and shut off all heat/ac/radio. On some they will run in the key position required for towing.