Science Questions with Surprising Answers
Answers provided by
Dr. Christopher S. Baird

How much money do I save by recharging my cell phone at work?

Category: Society      Published: February 27, 2015

By consistently recharging your cell phone at work (where your employer pays for electricity) instead of at home (where you pay for electricity), you save less than 50 cents a year.

According to Wikipedia, the iPhone 5 has a battery that can hold 0.00545 kiloWatt-hours of energy (about 20 kilojoules). Therefore, if you completely drain this phone's battery every day and completely recharge it everyday, it will consume:

0.00545 kiloWatt-hours x 365 days = 2.0 kiloWatt-hours

According to the US Energy Information Administration, residential electrical energy costs about 12 cents per kiloWatt-hour in the United States on average. Therefore, you would pay 24 cents a year to recharge your iPhone 5 if you drained it every day and recharged it every day at home. If you diligently recharged your iPhone 5 at work every single day rather than at home, the most you could ever save is 24 cents a year. Other cell phones have batteries with different capacities, but the difference is not large. No matter what type of cell phone you use, it costs less than 50 cents a year to recharge your phone.

cell phone
Public Domain Image, source: Christopher S. Baird.

As should be obvious, this amount of money is so small that forcing yourself to only recharge your phone at work is a waste of time and effort. Feel free to recharge your phone where ever it is the most convenient since it is effectively free. Also, this amount is so small, that you don't need to feel guilty that you are wasting your employer's money by recharging your phone at work. Your employer spends far more money on providing you with well-lit halls than with electricity to charge your phone.

If this low amount surprises you, perhaps you had little conception of the small amount of electricity that handheld devices actually use. In comparison to the 2 kWh used by your cell phone every year, a new refrigerator uses about 500 kWh a year. Older, less-efficient refrigerators use two to three times this amount of electricity. At 12 cents per kWh, it costs you about $80 a year to run a new refrigerator. Similarly, an electric clothes dryer uses about 900 kWh per year. A big household appliance tends to use about a hundred to a thousand times more electricity per year than a handheld electronic device. According to data complied by Efficiency Vermont, household items consume the amount of electricity per year shown below (the numbers are averages over typical products and users).

Household Appliance Electricity Usage Per Year (kWh)
Incandescent Light, 100W, 30 bulbs 3600
Portable Electric Heater 2160
Electric Baseboard Heater, 10 ft 1500
Swimming Pool Pump, 1 HP 1096
Electric Clothes Dryer 900
Freezer, 17 CF, auto-defrost, new 684
Television, 42-inch plasma 588
Refrigerator, 18 CF, new 492
CFL Light, 25W, 30 bulbs 360
Window Air Conditioner 270
Electric Oven 252
Dishwasher, Heat Dry 156
Microwave Oven 132
Clothes Washer 108
Desktop Computer 96
Dishwasher, Air Dry 96
Laptop Computer 12
Cell Phone 2

Looking at this chart, you see that if you really want to save money on your electricity bill, you should turn off unused lights, get energy-efficient light bulbs, avoid portable electric heaters, get rid of the swimming pool, hang your clothes to dry, and stop watching so much television. In contrast, you can use portable electronic devices as much as you want, since the electricity that they consume is a drop in the bucket compared to everything else in your house.

Christopher S. Baird is a physics professor at West Texas A&M University and author of the book, The Top 50 Science Questions with Surprising Answers.

Topics: battery, cell phone, charging, efficiency, electricity, energy, kWh, phone, power