There is a lot of videos across YouTube how to change battery in proximity beacons (big, blue one). It is quite simple as they are dedicated for such operation. But is that possible with stickers? Officialy not, but…
Lets see how looks single beacon sticker (usually few cm over few cm) and it is flat. So there is no option just to replace battery.
So the only option is to cut off the beacon and get the module working again (without rubber protection).
As you can see above removal is destructive operation (you may try to limit the effects of damage by less invasive cut however the rubber is very sticky and put on battery partially as well so that is very challanging operation). Still cheaper to change the battery than buying new one.
The biggest challenge was battery removal due to rubber (plastic) which kept it on place. With small help of a thin knife I moved the badge up and removed the battery.
The battery inside is quite unpopular CR2020 in Poland (I found them only on Aliexpress – the cheapest was 6 USD for 10 pack). CR2016 is too thin however CR2025 matches (CR2032 is too high).