How much does it cost to recharge the smartphone battery?

Have you ever wondered what are the costs for recharging your smartphone?

We are not talking about telephone top-ups, but about battery electric recharges and their impact on the "light" bill (or rather on the electricity bill).

We are going to perform some mathematical calculations that will give us an approximate data on the cost of the single recharge and also the annual cost that you will go to pay in order to supply to your device the necessary energy to its operation, but first because you don't try to guess the result?

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It's nothing complicated, but considering the great variety of devices on the market every specific case should be analyzed, for convenience we'll limit ourselves to using the technical specifications of the Nexus 4.

Required Data

The information to be found is:

  • Battery capacity and voltage.
  • Cost for each Kw that we can get from the electricity supplier bill (Enel, Eni, Edison etc etc ..)

It will probably be boring but a few lines of theory will serve to clarify the calculation method.

What interests us is to know what is the power absorbed by the device during a complete recharge of the battery, by definition the power is equal to the voltage for the current intensity and in our case to calculate it is enough to multiply the Battery voltage for his Capacity (Maximum value of electric current that can be stored inside it).

The units of measurement used must be comparable, so if we use Volts to indicate Voltage we will have to use Amps for Capacity (usually in the technical specifications of the devices the Capacity in MilliAmpere is indicated).

Charging Charges Smartphone

In our case the data relating to the Nexus 4 are:

  • 2100 mAh battery capacity equivalent to 2,1 Ah (Ampere / hour)
  • Battery voltage: 3,7 Volt

The power absorbed in each hour of charging is approximately equal to 8 Watt (2,1Ah x 3,7 V) and since it takes about 1 hour and a half to fully charge the power absorbed for a full charge will be of 12 Watt (8Watt + 4 Watt)

These are theoretical data that do not take into account the inefficiency of electronic devices, what is it?

Anyone who understands electronics knows that 100% efficiency does not exist, especially in chargers, this is because part of the power is dissipated in heat by the electronic components.

To consider theinefficiency of the charger, since I found nothing about it in the charger's technical specifications, we increase the absorbed power by 10% (probably a fairly optimistic calculation given that it is unlikely that a charger will have 90% efficiency but we are talking about ridiculous differences in terms of costs):

12Watt + 10% = 13,2 Watts

After establishing that for each full charge the Nexus 4 needs about 13.2W all that remains is to calculate how many euros we have to pay Enel to get this amount of energy.

In the last bill Enel I paid about 134 € for 586 KW, so I calculated the cost of every single KW:

134 €: 586 KW = 0,23 € each KW

1 KW is equivalent to 1000W, so each Watt costs 0,00023 €

We have everything you need to get the cost of a full charge, just multiply the cost of each Watt by the total Watts absorbed during charging:

13,2W x 0.00023 € / cent = 0,003036 €

Each top up of the Nexus 4 costs around 0,3 Euro cents, and assuming you recharge your smartphone every day the annual cost will be around 1,10 € (0.003036 x 365 days).

Did you answer the initial question exactly?

If you have suggestions or to report any errors in the method used, comment!

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