It is a good idea to keep spare batteries around for optics that require them. But don’t make the mistake I made and buy a bunch of the wrong type of battery and find out that you bought the wrong sort when you need one.
Many optics use 2032 sized batteries. My Insight MRDS red dots uses 1632. Unfortunately I had stockpiled 2016 sized batteries. Fortunately I was able to swing by a convenience store and get a bunch of the batteries I needed. Good thing I found out now.
On this topic, 2016 sized batteries have a very handy use. If you have a cheap or old optic that uses 2032 sized batteries, and isn’t very bight, you can stick two 2016 sized batteries in the place of a single 2032. This will cause the optic to run brighter. This will likely void any warranty, and should only be used as a short term stopgap until you can get a better optic.