Hi E S,
are you talking about the battery adhesive? If that is the case i can say - this sticker holds the battery in place and prevents it from moving around. If there is no sticker you might hear some noice when shaking the phone because the battery is moving. However it is unlikely that the battery disconnects because of that since the connector sits under a small metal shield. Depending on the phone movement theres a tiny chance that the battery or its cable deforms or gets damaged from moving around over time. It is not necessary to replace the adhesive with an original one, however i recommend using any double sided tape or similar rather than nothing.