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Understanding Chargers and Batteries – Watts, Amperes, Volts and mAh

Understanding terminologies

When we talk about smartphones, there are some important features that we must consider. Among these are size of battery and rate of charging. To understand these features better, Tech Bits Today dives into the details.

Understanding volts, amperes and watts

Chargers have 3 main characteristics: Volts, amperes and watts

  1. Volts: Unit of voltage. Measure of how fast or slow charges will move around in a loop. Voltage is required to move the charges from one end to another. Higher the voltage, the more quickly the charges will move.
  2. Amperes: Unit of current. It is the rate of flow of charges. The strength of a current is measured in amperes. The higher the amperes, the more quickly your phone battery will charge. Amperes are the defining factor between slow and fast charging.
  3. Watts: Watts is the unit of power. It is the energy created or used. It is the product of Volts and Amperes written as Power= Voltage x Current (P=VI)
Ipad Charger
Ipad Charger showing Watts, Volts and Amperes


Choosing the right charger for your phone

When choosing a charger for your phone, you need to look at the characteristics defined above: Volts, Amperes and Watts. Each charger has all three units listed on it. When looking up your phone charger requirements, you will see the charging watts in the battery specification area. Most chargers use 5V charging and different current ratings. As discussed above, current rating/Amperes are the defining factor for fast or slow charging.

What happens when you choose an unsuitable charger?

There can be four possibilities of choosing an unsuitable charger:

  1. Voltage too High: Charging at a higher voltage than required by the device is harmful. The device may shut itself down or overheat. You must not charge your device with overvoltage under any circumstances.
  2. Voltage too low: If the voltage of the charger is lower than the required rating, the device may not operate at all. This is because most chargers are rated 5V. If you use a charger less than 5V, it will not fulfill the requirement of output voltage required by the device (usually 4.2V). In this case, the device will not charge. In conclusion, chargers less than 5V output rating will not be able to charge your smartphone at all. However, if your device supports a higher voltage rating and you charge it at 5V or more, it will charge but relatively slow. Low voltage charging does not harm the device or shorten its battery life.
  3. Current too high: A higher current rating does not harm the device. In fact, it does not change anything. The device will draw the required current at the required voltage and charge smoothly.
  4. Current too low: Low current but the right voltage will charge your device slowly than normal. A lower current may also cause the adapter to overheat as the device draws more current from the adapter.

Battery capacity

The battery capacity of a cell phone is stated in mAh (Milli Ampere Hours). We can say that higher the mAh rating of a battery, the more electrical energy a battery can store. The unit mAh is calculated by multiplying the current (in mA) a battery discharges by the time it lasts. So, a 4000 mAh battery could power a device drawing 1000 mA current for 4 hours.

Iphone Battery Rating
Iphone 11 Pro Battery

How long a battery can power a device depends on the usage. The phone may draw more charge while playing games as compared to texting or listening to songs. Battery life may also depend on the processor and other electrical components in the phone. However, the most significant factor is the battery. While buying a new phone, check your battery mAh to see how much electrical energy it can store, the greater the mAh rating, the greater will be the battery capacity.

Battery Usage
Battery Usage displayed in iPhone

Larger batteries take longer to charge. This is where fast chargers come in handy. By providing more electrical energy (Watts), we can charge larger batteries in a shorter time.

Fast charging

Through this article, you must have gained enough knowledge to know what fast charging is all about. Yes, it all depends on the Power (Watts) of the charging. The greater the wattage, the faster the charging. However, it is not that easy! Not all smartphones can charge at a higher wattage. The phone’s circuitry must be able to support fast charging. Watts is the product of amperes and voltage. Manufacturers either tweak up the voltage or the current rating (or both) to charge the phones at a faster pace. For fast charging to work, all 3 things must be up to the required standard: Adapter, Cable and phone circuit design.

Fast Charging
20 Watt Fast Charger for iPhone

How long does it take to charge a phone with fast charger?

When fast charging, you can approximate how much time will it take your phone to charge completely. For example, a 15W charger operating at 5V 3A will take approximately 1 hour to charge a 3000 mAh battery (3A= 3000 mA). However, batteries charge exponentially, taking more time to charge the last 20%, therefore this can only be an approximation. In reality it may take 1.5 hours to charge from 0% to 100%. A good practice is to charge your phone battery to 70 or 80% and unplug.


Battery time is one of the most paramount factors in choosing a smartphone today. For this purpose you need to be tech savvy. Start with choosing the right mAh battery for your use. With this, check if the phone supports fast charging, if yes, then at what rate (CHECK THE WATTS!). After choosing the right phone, always make sure to plug in the right charger. Never use a charger with higher voltage and avoid using ones that have lower current or voltage rating.

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