battery charging time calculation

This blog is about battery charging time calculation. The same formula can be used to calculate battery discharge time.

I will let you know a basic formula with some examples.

Battery Charging Time

Battery charging time ( hour ) = Battery capacity ( In Ah ) / Current supplied ( In A )

Using this formula you can also calculate battery capacity or current.

Example 1


Battery capacity = 6Ah

Charging current = 2A

Charging time = 6Ah/2A = 3hour

Example 2


Battery capacity = 5000 mAh = 5Ah

Charging current = 1000mA = 1A

Charging time = 5Ah/1A = 5h

Similarly if we want to calculate the battery discharging time

Battery Discharging Time

Battery discharging time = Battery capacity ( In Ah ) / Current drawn from battery ( In A )

Example 3


Battery capacity = 10Ah

Current drawn = 2A (per hour )

Battery will be fully discharged in = 10Ah/2A = 5h

For better lifespan of the battery charging current Should be 30 % of battery capacity.

Suppose you have a battery of 10Ah then charging current should be 3A.

Your calculated value may not be accurate all time because most of the device now comes with adaptive charging that increases your safety. They detect your device ability to take specific current, the physical environment and sometimes the charging cable.

At last if we roughly talk about the charging voltage then it should be approximately 2v to 3 v higher than the battery’s rated voltage.

Safety tip : Although most of the chargers come with reverse charging protection, always check the polarity of charger before connecting it to battery.

Also try not to use battery when charging.

Some batteries are very sensitive. Always use a proper battery charger with over charge protection.


Frequently asked questions

  1. Can I charge 12 v battery using 5v charger ?
  • To charge a battery, we always need higher voltage than batteries voltage. Generally it is 2v higher.
  1. Can I charge 5v battery with 12 v charger ?
  • 12v is more than enough for a 5v battery. The battery will get over heated. In some cases it may explode. Depend on battery type.
  1. Can I charge 3.7v battery with 5v charger ?
  • As discussed above. To charge a battery we always need 1.5v to 3v higher voltage than battery, So 5v is accurate for 3.7v battery.
  1. What is the difference between Ah and mAh of battery ?
  • The term Ah means Ampere hour and mAh means milliampere hour.
  • 1Ah = 1000 mAh.
  1. Should i charge my new laptop for 8 hours ?
  • Its not necessary to charge it for 8 hour or any specific hour. Just charge it until it indicates fully charged.
  1. Which battery terminal to open ( disconnect ) first ?
  • It actually doesn’t matter which terminal of battery you disconnect first but in some specific cases like when disconnecting car battery you should disconnect the negative terminal first. Its because the negative terminal of battery is connected to metallic body of car ( car body is used as negative wire ). So if we disconnect the positive wire first then there will be chances that it will somehow get in touch with car body and short the battery.

Discover more –


Akash Sharma

Visit YouTube

Share This Post

1 thought on “battery charging time calculation”

  1. You only give part of the picture. Not all batteries are the same. And newer tech offers greater latitude with charging profiles. People need to understand how charging works. This is not just about figuring out how long it should take to charge my power bank or cell phone. It’s also about knowing what chargers are actually compatible with what devices.
    2A @ 5V is not the same as 2A @ 9V. 2A x 5V = 10W.
    A 10,000 mAh (10Ah/50Wh) charging at 2A x 5V should be fully charged in 5 hours. But the same battery charging at 2A x 9V (18W per hr.) should charge the same battery in 2.77 hrs. This how most “Fast Chargers” work. To determine if a charger is safe for your battery and/or device, check the Output profile of the charger against the Input profile of your battery/device.


Leave a Comment