Mobile & Electronics

Charging Cost Calculator

What it costs to charge a battery, counting the energy the meter sees rather than the energy that reaches the battery.

10 inputs Free, no sign-up

Your figures

If your battery is labelled in Wh, use this. Otherwise fill in the capacity and voltage below instead.

Together with the voltage below. Capacity alone is not enough - mAh measures charge, not energy.

Required if you gave a capacity rather than an energy.

Leave blank for this page's 85% assumption. Charging loses energy as heat in the charger, the cable and the battery.

Use fewer for something you only run at weekends.

Rupees per unit (kWh), from your own bill. Tariffs differ by state, by connection and by how much you use, so this is the figure the result is most sensitive to.

Try an example

Result

Your result

Enter your figures and the result appears here.

Estimates only. Rates, fees and specifications change. Confirm against the official source before you rely on a figure — see our disclaimer.

About this calculator

The energy that ends up in a battery is not the energy the meter counts. Charging loses some as heat in the charger, the cable and the battery itself, so a 37 Wh power bank pulls around 43 Wh through the socket.

The honest headline is how small the answer is. Charging a phone every day for a year costs a few tens of rupees — and knowing that is more useful than a vague sense that it must add up.

How to use this calculator

  1. Enter the battery energy in watt-hours if you have it, or the capacity and voltage together if you do not.
  2. Set the efficiency if you know it, or leave the page's 85% assumption.
  3. Enter how often you charge and your rate per unit.

The formula

Energy into battery = Capacity (Ah) x Voltage
Energy from socket  = Energy into battery / Efficiency
Cost per charge     = Energy from socket in kWh x Rate
Monthly cost        = Cost per charge x charges a month

Dividing by the efficiency, rather than multiplying, is what makes the wall figure larger than the battery figure. Getting that the wrong way round is the commonest error in this calculation and it understates the cost.

SymbolMeaningUnit
Battery Wh Energy reaching the battery Wh
Efficiency Share that survives %
Wall Wh Energy the meter counts Wh
Rate Your tariff per unit Rs/kWh

Worked example

A 37 Wh power bank charged daily at 85% efficiency, ₹8.50 a unit:

Into battery = 37 Wh
From socket  = 37 / 0.85 = 43.5 Wh = 0.0435 units
Per charge   = 0.0435 x 8.50 = Rs 0.37
Per month    = Rs 11.10
Per year     = Rs 135

Notes and limits

  • Battery energy and wall energy are different figures. The meter always counts the larger one.
  • A charger left plugged in with nothing connected still draws a small amount — a fraction of a watt to a watt or so. Small per hour, but it runs every hour.
  • Charging efficiency falls somewhat at high currents, because more energy becomes heat. Fast charging costs marginally more per charge.
  • The answer being very small is the honest result. Charging habits are not where an electricity bill is decided.
  • For a phone specifically, the phone charging cost calculator asks the same questions in phone terms.

What this calculation assumes

  • Each charge is a full one from empty; a partial charge costs proportionally less.
  • Efficiency is your figure or this page's 85% assumption.
  • Idle charger consumption is not included.

Frequently asked questions

How much does it cost to charge a power bank?

For a 37 Wh (10,000 mAh at 3.7 V) pack at 85% efficiency and Rs 8.50 a unit, about 37 paise per full charge - roughly Rs 11 a month if you charge it daily.

Why is the wall energy higher than the battery energy?

Because charging is not lossless. Some energy becomes heat in the charger, the cable and the battery. At 85% efficiency, 37 Wh into the battery means about 43.5 Wh out of the socket.

Does leaving a charger plugged in cost anything?

A little. An idle charger draws a fraction of a watt to a watt or so - measured in single rupees a year for one charger, though a household with many adds up more noticeably.

Is fast charging more expensive?

Slightly, because higher currents mean proportionally more energy lost as heat. The difference is small in absolute terms given how little a charge costs.

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