Battery life expectancy during long periods of sitting unattended.

[LymanT]

I drive a semi over the road, and am gone for 2 to 3 months at a time. The vehicle is in a secured area, but even with the low voltage battery saving feature, I wonder how long I can go without charging the battery. I can always remote start and stop the car using FordPass, but how often, and for what period of time should I let it idle before I can consider the battery charged. Since most cars don't really provide a charge until above idle, will that even be a feasible alternative? I have considered getting a battery cutoff switch or disconnecting the negative terminal while away, but that defeats the purpose of having an alarm system.
Thoughts and answers?
Thanks!