In addition to confirming what you've already been told, i buy CR2032 batteries in packs of 10 from ebay for about 2 or 3 quid a time. Yes they're not fantastic but usually branded as Maxell or Panasonic or similar and for the cost you can't go wrong when the likes of Halfords, Sainsburys, Timpsons are all £6-7 per battery!
https://www.ebay.co.uk/itm/314572810753
I keep the spares in the drawer ready for when the battery gets low but usually use the spare fob for a few days every so often just to see if there's any difference in performance of the fobs and also to ensure the spare fob remains coded.