^^^ Ruddy 'eck! You're right, Alavahalf! (That'll teach me not to trust the first Google link I look at!).
SORRY, Stanbesida!
As I correctly indicated above though, 18650 batteries are rechargeable. So you need to check your doorbell's instructions to see how you're meant to charge them. If you really need to replace your batteries though (because they're no longer accepting a charge) see here for replacements:
https://www.batteriesplus.co.uk/acatalog/copy_of_Lithium_Ion__Li-Ion___3.7V_Batteries-1.html
If you need a battery charger, see here
Amazon.com User Recommendation
Apologies again for the duff info (and thanks, Alavahalf)!