Battery Size Calculator: Know The Battery Capacity at Its Best

Before you use a battery or plan to purchase one, it’s better to know the amount of energy the power cell can store at a particular temperature according to its charger and discharge rate as well as current values.

Whether looking for Alkaline, Nimh, LiPo, or Lithium batteries, the calculation principle of current, capacity, charge, discharge, and power remains the same.

Let’s look at some essential information and formulas to help you precisely measure a batter size.

Why Battery Size Calculator Is Essential

A battery size calculator tells you the battery’s remaining capacity, aka battery size, and the load current the device can draw from it. If you know these two pieces of information, selecting the correct battery for a particular purpose will be easier.

Our battery calculator can advise you on the best battery to use based on the power requirements of your device and the length of time you plan to have it active. This tool aims to determine a battery’s ideal AH (Amp Hours) rating, ensuring it is not discharged to an unsafe level.

And the same goes for almost anything that uses a battery.

Battery Size Calculator

Battery Type
Load Time (Hour)
Battery Load Unit
Current Charge (%)

How to use the Battery Life Calculator

  1. Select battery type between Lead acid and Lithium-ion
  2. Input the battery load time in hours
  3. Select battery load unit either in watt or ampere
  4. Select the desired discharge percentage for a particular battery

Tips on Battery Discharge

  • Don’t 100% discharge lead-acid and lithium-ion batteries.
  • Lead-acid batteries should be discharged up to 50%.
  • Lithium-ion batteries should be discharged up to 20 percent.
  • Lithium-ion batteries store more energy per unit of weight (energy density) than lead-acid batteries.
  • In terms of output, a lithium-ion battery can outperform a lead-acid battery of the same size.

Battery size for a Lithium-ion battery

To know the size of a Lithium-ion battery, you need the load current, duration, and remaining charge. The formula is as follows.

 BLi-ion = 100. I. t / 100-Q

I = current in ampere.
t = duration in hours.
Q = required remaining charge in percentage.

Battery size for a Lead-acid battery

Like the Lithium-ion battery, you will need the load current, duration, and remaining charge data to calculate the battery size.

Blead-acid = 100.I.t / (100-Q) (0.02t + 0.06)

I = current in ampere.
t = duration in hours.
Q = required remaining charge in percentage.

Definitions that you will find helpful

You perhaps know all the terms already. However, if there is doubt, the following definition will freshen up your memory and help you do that math perfectly. 

Battery Current

Battery current is the amount of charge that a battery can displace from one point to another. The formula is as follows.

Current I = Powe in watts / Voltage in DC Volt

Battery configuration for voltage

  • Add the voltage of individual batteries in the case of a series-connected battery pack to calculate the voltages of its individual cells.
  • Inverse the voltage of each battery and add them in case of a parallel-connected battery pack to get the total voltage of the pack.

Battery Life (Required Duration)

Battery life is the estimated remaining duration of the battery using its nominal capacity and the average current being drawn from it.

Battery Life = Battery Capacity (mAh)/Load Currrent (mA)