Actually I read the rechargeable section but there is no explicit mention there of how quickly does the rechargeable battery provide power. Is this implied that it's not in quick bursts because it's rechargeable? Or maybe I missed something? (I re-read the section again now).
Yes, there is no mention because it's not very different from other technologies.
Molten salt batteries are mostly not practical (who wants to carry around some explosives at boiling water temperature), but the single use cells get some usage because of this feature. Rechargeable ones don't.