Enter the power consumption, battery capacity, and battery voltage into the calculator to determine the backup time for your battery system. This calculator helps you estimate how long your battery can run a particular device or system.

Battery Backup Time Formula

The following formula is used to calculate the battery backup time.

B = (C * V) / P


  • B is the backup time (hours)
  • C is the battery capacity (ampere-hours)
  • V is the battery voltage (volts)
  • P is the power consumption (watts)

To calculate the battery backup time, multiply the battery capacity by the battery voltage and then divide by the power consumption.

What is Battery Backup Time?

Battery backup time is the duration for which a battery can provide power to a device or system before it is completely discharged. It is a crucial factor for systems that require a reliable power supply in the event of a power outage, such as emergency lighting, medical devices, and backup power systems. The backup time depends on the battery’s capacity, its voltage, and the power consumption of the connected device.

How to Calculate Battery Backup Time?

The following steps outline how to calculate the Battery Backup Time.

  1. First, determine the power consumption (P) of the device or system in watts.
  2. Next, determine the battery capacity (C) in ampere-hours.
  3. Next, determine the battery voltage (V) in volts.
  4. Next, gather the formula from above = B = (C * V) / P.
  5. Finally, calculate the Battery Backup Time (B) in hours.
  6. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

Power consumption (P) = 120 watts

Battery capacity (C) = 100 ampere-hours

Battery voltage (V) = 12 volts