Sealed batteries still have vents to prevent over pressure sufficient to rupture the case. They are just what's called calve regulated, as in not open to atmosphere normally, which is how the old style vents are.

Even AGRs will have them and they will still vent acid if they pop open. How much is really irrelevant since it will damage your stuff anyway.

A bad regulator that full fields your alternator will take any battery out if run long enough. Lost an Optima that way back in the 90's and yes, the vents vented.

A lithium battery is a bad choice unless your charging system is designed to charge lithium batteries. They are different.