I've heard this story about glow engines firing without the battery connected, a couple of guys who've mentioned it are very well respected so there must be some truth in it. However, in my 40+ years of messing around with various engines I've never experienced it and neither has anyone else that I know so I'd guess the chance of it happening is about as good as being hit by a meteor

Rossi, ST etc aren't what you'd call really high compression...they're about 11:1 where OS and so on are about 9.5:1 which isn't that much different. I run my Enya 60X at 13.5:1 and it definitely never shows any sign of kicking without the battery.