Certain ranges of the electric models are supplied with a battery back-up in the rear of the transformer. This battery is for emergency use only and will cut in if there is a power failure (it will need replacing after this). The battery will have a lifespan of approximately 6 months in standby mode and therefore must be changed regularly.
The purpose of a battery backup is to ensure that in the event of a power cut you are still able to operate the chair- this is important if you are fully reclined at the time of the power cut as it may be impossible for you to get out of the chair. Most chairs come with a battery backup as standard or it is offered as an optional extra.
Important: The battery backup is a safety feature to return the chair to a sitting position in the event of a power cut. It will only operate a limited number of times, after which the battery will need to be changed.