HI Joe. Yes, I have walked off and left the ignition in the same position as you on my soft top ND shortly after I first had it, and even more absent mindedly I also forgot to connect the smart charger, net result, flat battery. However if I do things correctly no problems, and it’s now just over 5 years old. So don’t worry too much, it’s not something going wrong it’s just caused by the design of the system. Also it’s worth remembering that every time you start the car you need to drive around 6 - 8 miles to replace the energy used by the battery, so if you’re doing short journeys be careful. Get a “smart” charger if you haven’t already got one! Good luck!
Roger