Answer: A) Battery backup
Explanation:
A battery backup are used to provide the source of power backup to various hardware components and desktop computers. In many cases, the devices are plugged into UPS ( uninterruptible power supply) for backup power and it is also depend upon the size of the UPS.
All the battery backups are located inside so that is why, the devices are heavy in weight. Usually, the battery backup front required additional button for performing various functions.
And the battery backup devices are manufacture by using the varying degree of backup abilities.