Confirm you fitted the right cell
Wrong size or chemistry is the most common miss — for example AAA in a remote that needs AA, or alkaline LR44 where the device wants silver oxide.
Open the family hub for your product (TV, Bose, garage, AC) and match the generation or part number before buying another pack.
Polarity, contacts and rechargeables
Match the +/− marks. Clean dirty contacts. Some makers (including Bose for several soundbar remotes) advise against rechargeable cells because of lower voltage.
Pairing and line of sight
Bluetooth / Magic / voice remotes may need re-pairing after a battery change. IR remotes need a clear path to the device.
Garage transmitters may need re-learn at the opener if the remote itself was replaced — that is separate from the battery step.
When the remote is dead
If tray-correct fresh cells still fail, the next step is a replacement remote for that part number — not a random universal remote labelled “compatible” without checking feature coverage.