In order to calculate how long a battery can be fully recharge, that depends on the mAh of the battery.The **mAh **specification of a battery or any device simply means milliampere-hours. mAh is the amount of milliamperes which a battery can supply to a circuit or device for one ha battery also how long a battery will will be able to last in a device or circuit.

If a battery has a mAH specification of 2600mAH,it means it can provide 2600mA (milliamperes) for one hour. Likewise a battery with a mAH specification of 20,000mAh can provide 20,000mA for 1 hour.

## How to calculate how long it will a battery to be recharge.

This depends on two factors which are

• The mAh of the battery

• The mA of the charger.

If the mAh of a battery is 3000 and has to be recharged. The time taken for the battery to be fully recharged depends on the mA of the charger. Let say the mA of the charger is 600mA and is to used to recharge a 0% battery of 3000mAh,it will take 5hours to fully recharged the battery.

Thus,3000mAH battery can be recharged in the following ways:

800mA charger will take 3.75hrs

1000(1)ma charger will take 3hrs

1500(1.5)mA charger will take 2hrs

2000(2)mA will take 1.5hrs

### Thus, we can conclude that the time taken for a battery to be recharged is directly proportional to the mAh of the battery and inversely proportional to the mA of the charger provided there is no energy loss.

Practically, this estimation will not be true due to energy loss through heat and resistance and also if the battery is in use . That is why it is advisable to turn your device while recharging it. Even so, there will be still be energy loss.

In the same way, a battery/power bank with higher mAh values will last longer than a battery with lower mAh values.

In order to determine the number of times a power bank can recharge a battery, it all depends on both the battery’s capacity and the power bank capacity. If you a power bank of 30,000mAh which will be used to charge a battery of 3000mAh, the number of times the power bank can charge the battery will be 10 times(power bank mAh value divided by battery mAh value).

So the higher the mAh value of the power bank, the better in terms of the number of times you can use it before it is exhausted. Also note, the higher mAh value of the power bank, the bigger and heavier it will be.

Unfortunately the value of mAh is not the whole story. If mAh is all that matters, that means you can use a laptop’s power bank to charge a phone’s battery. Another essential factor to consider is the voltage. The standard voltage of a phone’s battery is 3.7V and the standard output voltage of every phone’s power bank is 5V. 3.7V is just a nominal, average voltage of a li-ion battery, the actual voltage of a fully charged battery is 4.2V. As the battery is used, the voltage will drop lower and lower until the minimum which is around 3.0V.

### Why is the output voltage of a power bank 5V and not 3.7v you may ask. If the output voltage of the power bank is the same with the value of phone’s battery. Then your phone’s battery will be charging the power when the voltage level of your phone’s battery is greater than that of your power bank.

Below is a table in order to understand the concept.

3V – 0%

3.12V – 10%

3.24V – 20%

3.36V – 30%

3.48V – 40%

3.60V – 50%

3.72V – 60%

3.84V – 70%

3.96V – 80%

4.08V – 90%

4.20V – 100%

Now imagine your power bank has only 10% left and your phone is 40% charged, if you connect your power bank to your phone, then your phone will be charging your power bank because of the voltage difference(3.12V vs 3.48V).