# How to Calculate Battery Backup Time

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Battery backups are commonly used in offices or locations where it is important to keep critical systems up and running in the event of a power outage. As long as the electricity is flowing normally, the battery pack sits quietly out of the way, but the moment the electric flow is interrupted, the battery will kick in as a back-up source of electric power. The amount of time the battery lasts depends on the power consumption of the devices attached to it. Calculating the back-up time of the battery is easy, once you have identified a few key variables.

### Things You'll Need

• Pen
• Paper
• Calculator
• Determine the power efficiency factor of your battery backup. The battery uses a DC-to-AC converter. This converter stores live current in a rechargeable battery pack, then transforms the stored energy in the battery into electric current for the electronic devices attached to the battery backup. Refer to the power information label or the user's manual to identify the power efficiency factor of the converter.

• Identify the ampere hours (AH) for your battery backup. Refer to the power information label posted on the backup to obtain the AH information, which is typically reflective of the voltage of the battery. In the case of multiple battery backups combined into one system, identify the AH for each backup, then add all of the numbers together to identify the combined total number of ampere hours.

• Multiple the ampere hours of the battery backup by the amount of the power efficiency factor. Multiplying these numbers results in a number that reflects the voltage output of your battery backup system.

• Refer to the power supply or the user's manual of the devices connected to the battery backup system. The power supply should contain information to identify the voltage and amperage of the device. Multiply these numbers together to calculate the devices power consumption according to volt amperes (VA).

• Type the device power consumption number into a calculator. Divide the number by the amount of the voltage output of the battery backup. Dividing these numbers will tell you how much electric current will be drawn through the device.

• Press clear on the calculator and type in the amount of the power efficiency factor that was determined at the start of the process. Divide this number by the amount of electric current drawn. Dividing these numbers will tell you the maximum amount of time that the battery backup will provide electric current to the devices. This time is calculated in hours.

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