Power Indicator

...remember to close the doors only if absolutely necessary. Gotta conserve power. The  is a vital in-game mechanic which displays the amount of power remaining, and the amount of power that is currently being consumed by showing the speed at which power runs out.

In-Game
The Power Indicator is a major game mechanic that is located at the bottom left of the player's screen. It starts off with 100% power; however, the value is rounded down to the nearest integer making it appear to start at 99% (which is also the reason the amount of power left will read 0% for a while before actually shutting down). It will decrease at a speed depending on how much power is being used at any given time.

For example, having two doors closed and having the monitor up will cause the power to drain at an alarming rate. Conserve power by using the lights, doors, and cameras sparingly. Below the percentage indicator is a usage graphic that shows two green bars, a yellow bar, and a red bar. If only one or two green bars are illuminated, then the power usage is minimal. If the yellow bar is illuminated, then power usage is medium, and the red bar indicates critical or max power usage.

What Drains Power

 * There is an unstoppable 1-bar drain that drains 1% power every 9.6 seconds, seemingly caused by the fan and the light in the office, the security cameras running and the lights around the building.
 * Turning on the lights, closing the doors, and checking the Monitor will cut that time in half for each one turned on. 1% each 4.8 seconds with 2 bars, an average of 1% each 3.2 seconds (in a cycle of 2.8s, 2.9s, 3.9s) with 3 bars, and an average of 1% each 2.4 seconds (in a cycle of 1.9s, 2.9s) with 4 bars (the max amount). It is possible to have 5 bars, but this only lasts for less than a second after closing both doors, turning one light on, and checking the cameras. It should be noted that these values tend to fluctuate over the nights, possibly intentionally to make the game harder in later nights or as a side effect of additional processing for more active animatronics.
 * The first time Mei Hua is blocked, she drains 1% power. The second time she is blocked, she drains 6% power. The third time she is blocked, she can drain the power upwards of 11%.

Power Usage Calculations
~9% power used per in-game hour with the constant 1-bar usage. Assuming a night where no one kills the player (only possible if Foxy and Freddy never attack the entire night even without being looked at), the maximum amount of power capable of completing a night with is ~45% (Upper limit high-score).

Assuming the Camera, Doors and Lights all drain the same:

Not accounting for the few seconds the player has to survive with no power, even distribution of power over the 6 hours would lead to ~16.6% power usage per hour. Below is a guide of values to try to remain above. (Tip: Energy can be conserved earlier in the night due to having a slight grace period before the Robots start bearing down on The Office. This only works well during the first few nights, however.)
 * 18% power used per hour with constant 2-bar usage. Electricity would run out at ~5:30 AM.
 * 27% power used per hour with constant 3-bar usage. Electricity would run out at ~3:42 AM.
 * 36% power used per hour with constant 4-bar usage. Electricity would run out at ~2:47 AM.


 * 12am: ~99%
 * 1am: ~83%
 * 2am: ~66%
 * 3am: ~50%
 * 4am: ~33%
 * 5am: ~16%
 * 6am: ~0%

Trivia

 * There is not an endless supply of power because the restaurant is apparently on a "power budget", due to their low revenue in the past few years.
 * The unstoppable 1% drain is most likely due to the lights around the building, and the fan in the office.
 * It is unknown as to why, when the player runs out of power, only Tiwa and Nasissa can kill them (the power outage does not cancel Nasissa's death scene).
 * Mei Hua's sprint and attack can be cut off by the power going out, as seen at 5:55, in this.
 * Using cheat mode in the Android version of the game prevents power from draining.
 * However, this does not make the player invincible, as animatronics can still get in if the doors are not closed. Even if both doors are closed, Nasissa can still get in the office if she is summoned using his West Hall Corner poster.