The battery must be removed by desoldering the two positions shown. Take note of the polarity of the battery before removal.

Desolder the points and remove the battery.

Solder the new battery in place, maintaining polarity.

New battery installed here - the new battery had a plastic ring around it. The tabs may be in slightly different positions and may require manipulation to fit into the existing location

Once the battery has been connected, check the display panel to see if the clock is flashing - this will indicate the battery is connected.