Warnings against charging batteries indoors is that they can emit gas that can be very explosive. However, after owning a boat for several years, with constant need to charge many very big batteries, I just figured that the warnings must be vastly excagurated when it comes to motorcycle batteries.
However, I did stain a kitchen counter charging a battery. The battery had a small hole to vent the battery when it got hot, as they do when you charge them. Vapour condensated and dripped onto my synthetic counter and left a small stain that did not clean out. I no longer charge my batteries indoors, much like I don't service my bike indoors.
I wouldn't be tto conscerned about charging batteries indoors though, but I would put something underneath it, like an old tray or something.
That much said, I'm not an expert on the matter, it is just my novice opinion when I say "go ahead".