This guide is taken from the Aico website - how to change the battery in your alarm? - tips for homeowners.
The alarms that are in your home will most likely be wired into (and powered from) the mains power, but are likely to also have a built-in battery back up to power the alarm if the mains fails.
There are two main types of battery back-up - Rechargeable Lithium and Alkaline.
The Fire Alarms with a Rechargeable Lithium back-up will never need their battery changing as the back-up is designed to last for the lifetime of the alarm (10 years).
Alarms with this type of back-up will have a sticker on the front, like that shown below.
Remember: on the Sticker it needs to say, Rechargeable Lithium back-up

Typically, the battery will last around 3-4 years in standby but the alarm will beep once a minute to let you know when the battery needs changing. The battery is built-in to the back of the alarm, so the alarm will need to be removed from its base-plate (which is the only part actually fixed to the ceiling) before the battery can be changed.
Removing the fire alarm
Step 1: Turn off the mains power to the alarm. To do this, have a look on your fuseboard/consumer unit for a circuit marked 'Smoke Alarms' and turn this circuit off. The green light on the alarm should go out.

Step 3: With the screwdriver still inserted, slide the bottom half of the alarm horizontally away from the screwdriver. It should move across slightly.
Step 4: Now the alarm is released from the base-plate and is free to be removed.
Note: The base-plate will still be fixed to the ceiling as this is the part that is wired into the mains power.
Replacing the Aico Fire Alarm Battery

Refitting the Aico Fire Alarm Battery
