Larian Studios Forums Divinity - Original Sin Divinity Original Sin - Help/Tips/Tricks What is charisma xp for?

That's the Charisma skill... something differently entirely again.

But yes, the XP is simply there as alternative for the combat XP you would have gotten, since most rolls are to avoid combat.
It generally gives far less than killing though, and can be exploited in several cases by getting the XP and then force attacking them anyway.