How to Calculate Your Power Needs

Lightning over a neighborhood and the power is out
A power outage can be an inconvenience for many, however for people who depend on life-saving medical equipment, even small power outages can be life threatening. Thoughtfully sized battery backup systems can save lives and allow people live independently. Battery capacity isn’t the only consideration though. Understanding the features and options available is also important.

Understand your power requirements

What's a Watt?

Watts tell us how much power a device uses in the moment. For example, a brighter light bulb uses more Watts than a dimmer one.

Watt Hours Are Important

Watt hours (or watts per hour) tell us how much power is consumed over time. Battery system capacity is mostly measured in Watt hours. Calculating Watt hours is easy. Simply multiply the power of the device (Watts) by the hours used each day.

How do you find out how much power a device uses?

Well, that’s a bit tricky. You can:

  • Look in the user manual,
  • Google it,
  • Call the manufacturer,
  • Purchase a power meter (most accurate), or
  • Explore our power calculator which provides power and consumption estimates for several different types of life-sustaining medical devices (least accurate).

Line drawing of a user manual

What about amps and volts?

Now you are getting into electricity 101!  Amps refer to the flow of electricity through a wire. Volts refer to how fast the flow of electricity moves through the wire. If you know the values for both amps and volts, the formula for calculating Watts is easy:  Amps x Volts = Watts

caution Finding accurate voltage information for your device might be a challenge. So when in doubt, use the strategies from the list above to find out how many watts your device uses or consult with a qualified electrician.

Putting it all together

Calculate Your Total Power Consumption

Add up the Watt hours (consumption) for each of your important devices . The result will be your power needs per day. You can use this number to shop for the correct size battery backup system. 

A Sample Calculation

 My DevicesPower

(Watts x Time)
Oxygen Concentrator300 watts8 hours2400 Wh
Medical Refrigeration75 watts8 hours (33% duty cycle)600 Wh
Infusion Pump60 watts40 minutes26 Wh
Mobile Phone--12 Wh*
Total  3,038 Wh
*Charging a mobile phone consumes about 12 watt hours each day.

Considerations When Sizing a Battery System

  • You will never get the rated capacity of a battery system. Expect 80% - 90% of the rated value instead.
  • Bigger isn't always better. Large batteries can be very heavy and may be difficult to transport if an evacuation is required.
  • Smaller backup batteries can provide the extra time needed to plan and evacuate if necessary. Just a few hours can be enough to get you to a safe location with power.
  • You can often purchase add-on batteries to increase the capacity of a smaller battery backup system.
  • Choose a battery which fits into your emergency back up plan.
  • Product features and options may be as important as the size of the battery system. 


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CU Denver

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Suite 130

Denver, CO 80204


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