I think the watch function is complimentary, so when the device can't vape anymore, you chuck the entire thing in the bin.
I just want to add that, in my experience, all internal battery devices keep finding novel ways to end their services well before the battery reaches the cycle-end-of-life (100 full cycles give-or-take).
I'm am going to pass on this one. It reminds me of a (Swan-song) mod device, the one with an embedded Bluetooth speaker - which had a similar, very narrow market acceptance.
Things may be different in the Far East of Asia, where the novelty and impulse-buys are still strong market drivers.