Most buildings back up only a limited load per home, lights, fans, the lift, and perhaps one socket, rather than heavy appliances like an air conditioner or a geyser, unless a home has paid for a larger share. It is billed apart from the regular electricity bill, on its own meter or a flat charge, and the amount varies from one building to another depending on the generator's size and how often it actually runs. We ask how a building bills for backup power, rather than assuming one building's rate applies to another.
The number
none, billing varies too widely by building to state a single figure responsibly
Sources
Where it comes from. Level 1 is a government or court page, level 2 established press, level 3 a portal's explainer, which gives only what is commonly quoted.
- Power backup and electricity guide for Whitefield apartments, https://www.prestigeswhitefield.com/whitefield/power-backup-electricity-guide.html, level 3