Voltage Current Resistance and Power

Our phones run on electricity provided by the batteries inside them. We cannot understand how batteries work fully without understanding some battery specifics like voltage, current, resistance and power. These concepts are very key to how batteries operate and how you can care for them.

Understanding the concepts of voltage current resistance and power would go a long to helping you know what type of charger to get for your device, the length of a cord needed for faster charging, battery voltage and power ratings etc.

So lets look at each of them one by one.


This can be defined as the force or pressure that forces charged electrons (current) to flow from a region of high electric potential to a region of low electric potential.

Voltage is what make electric charges move. It is the “push” that causes electrons to move from point A to point B.

Think of it as this. Let’s say you have two gallons, one empty and one full of water. If you place the full gallon on a table and empty one on the floor and placed a hose into the two of them. Water is going to flow from the full gallon to the empty one. The force pushing the water out of the full gallon and into the empty one can be thought of as voltage.

Voltage can also be said to be the difference in electric potential between two points and is always measured between those two points e.g. the positive and negative terminals of a battery, an electric wire and its load etc.

Voltage is also known as Electromotive force (EMF). The unit of measurement of voltage is the Volt (V), named after Alessandro Volta.

Voltage can be calculated by multiplying current by resistance

V = i x r


  • V = voltage
  • i = current and
  • r = resistance

Voltage in batteries is a constant however as it is a manufacturing standard and all equipment supplying power have to abide to it. The standard voltage for primary disposable batteries is 1.5V, USB connections are 5V, smartphone batteries are 3.7V (with max charge voltage of 4.7V) and 110V to 220V for heavier electronics.


An electrical current is a stream of charged electrons moving through an electrical circuit or conductor. You can think of a circuit as a one-way road and the electrons as cars that ply the road. A steady movement of cars will produce traffic right? That is how electrons move too, and a steady electron movement is called current.

Current is what provides the electrical energy that electrical appliances use to do work. Voltage is the force that pulls current from the source to the receiver.

There are two type of current:

  • Alternating Current (AC) and
  • Direct Current (DC)

Alternating current (AC) is a type of current that periodically reverses its direction of flow because it operates using a sine wave. It is very useful for transferring electricity over long distances.

Direct current (DC) is a type of current that only moves in one direction. DC is the current used in our household appliance and of course, our phones.

Current is measured in Amperes (A).

It can be calculated by dividing voltage with resistance.

i = V/r


  • V = voltage,
  • i = current and
  • r = resistance


Resistance as the name implies is the opposition to the flow of current through a conductor e.g. a wire. Every material no matter how conductive has some resistance to the flow of current. The longer the wire you use for conducting electricity e.g. charging, the higher the resistance. Increased resistance to current flow will see a reduced output in charging speeds due as energy will be lost as heat.

Resistance is measured in Ohms. In Physics, you can use Ohm’s law to solve for resistance as it states that electric current is proportional to voltage and inversely proportional to resistance. That is Ohm’s law = i ∝ V

r = V/i


  • V = voltage,
  • i = current and
  • r = resistance


Electric power is the rate or speed at which electrical energy is transferred through a circuit and into a load. If a wire, a generator or a battery can transfer a lot of electrical current very quickly, it is said to have a lot of power.

The unit of measurement of electrical power is in Watts (W).

The power of an electrical source such as battery or charger can be calculated by multiplying the voltage and the current delivered.

P = V x i


  • V = voltage,
  • i = current and
  • P = power

This is why many chargers are rated in watts.

Thank you for reading to the end. As always, ensure to check out our links for more information and…


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