Note: I have tried for 15 minutes to get a quote from the previous post to be included with my reply but it fails EVERY time. It's the same kind of error that happens when there is a percent sign present.
I can see no reason that it should do that.
I'm sorry but I don't agree with that at all. My experience has been exactly the opposite.
In a bike that has ZERO parasitic drain, you can fully charge an AGM battery and leave it out in the cold for 3 months with no appreciable change......as evidenced by the fact that a "smart" charger connected to it after that time reports a full charge after only about two minutes. I've had them last OVER 5 years being treated like that.
I don't recommend, however, that you ever ASSume what is going on and just leave any battery completely unattended for over 30 days. You need to check it and charge as necessary....until you really determine that it doesn't need charging, that is.