Not much. In fact, probably less than a penny!
You can roughly guesstimate it for yourself this way:
Note that electricity is usually sold by the kiloWatt hour (kWh) — 1000 Watts delivered for one hour.
If you know the Wattage of your phone charger, and how long it runs, you can very easily calculate how many kWh it uses, and thus, the cost.
Look on your phone charger’s housing or plug: The fine print there might list its Wattage; but if not, it almost surely will list the charger’s output Amperage (A) and output Voltage (V). That gives you the Wattage because [Amps × Volts = Watts]
So:
(charger’s rated output Amps) x (charger’s rated output Volts) = (charger’s nominal Wattage)
If your charger is rated for, say, 2 Amps at 5 volts, the equation becomes (2) x (5) = (10); the charger consumes a nominal 10 watts when it’s running.
Run a 10 watt charger for an hour, and you’ve consumed 10/1000 of a kWh; or 0.01kWh.
Let’s say your phone takes 4 hours to fully charge. That would consume
4 x 0.01kWh, or 0.04kWh.
If you pay $0.15 per kWh, that electricity costs you $0.15 x 0.04, or just 6/10th of a cent!
BUT there are a million variables the above simplified guesstimate doesn’t cover. For example, there’s energy loss (to heat) at both the charger and battery. Many newer quick chargers support and switch among several levels of voltage and amperage, depending on the battery state; and almost all chargers will slow or stop themselves once the phone approaches full charge. Etc.
All of these things alter and complicate the equation above the ultra-simplified example I used.
But the core idea remains the same: Charging your phone is not a major expense, and is not likely to have a meaningful impact on your budget.
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