This all-in-one online Battery Capacity Calculator performs calculations using a formula that relates the battery voltage and capacity to the energy stored in the battery. You can enter the values of any two known parameters in the input fields of this calculator and find the missing parameter.
What is Battery Capacity?
Battery capacity is a measure of how much energy a battery can store and deliver. It represents the total amount of electric charge a battery can hold and is typically expressed in ampere-hours (Ah) or milliampere-hours (mAh).
Battery capacity indicates the maximum amount of energy a battery can provide under specific conditions. In practical terms, it tells you how long a device can operate before the battery needs recharging or replacement. For example, a 2000 mAh battery can theoretically deliver 2000 milliamperes (or 2 amperes) of current for one hour, or 1000 milliamperes for two hours.
Capacity is influenced by several factors, including battery chemistry (e.g., lithium-ion, lead-acid, nickel-metal hydride), temperature, rate of discharge, battery age and health. It’s important to note that the rated capacity provided by manufacturers is typically measured under ideal conditions, and real-world performance may vary.
Battery Capacity Formula
Battery capacity, being the current capacity of a battery, is defined by the formula:
For example, if a device draws 500 mA of current and the battery lasts for 4 hours, then its capacity is 500 mA × 4 h = 2000 mAh or 2 Ah.
In energy terms, battery capacity is also linked to voltage. To determine the energy stored, measured in watt-hours (Wh), the formula is:
So a 12V battery with a 100 Ah capacity can theoretically provide 12 V × 100 Ah = 1200 Wh or 1.2 kWh.
This last formula is used in our Battery Capacity Calculator.
Use and Importance of Battery Capacity
Battery capacity is essential in determining how long a battery can power a device or system. It helps match energy supply to demand, especially in applications like renewable energy storage, electric vehicles, and portable electronics.
A higher capacity generally means longer run time, fewer charge cycles, and better reliability – vital in both everyday devices and critical systems like medical equipment or backup power.
It also aids in sizing energy systems: knowing the total energy requirement allows users to choose batteries with sufficient capacity. However, higher capacity often comes with trade-offs such as increased size, weight, and cost. Accurate capacity assessment is thus key to balancing performance, efficiency, and practicality.
Related calculators
Check out our other physics calculators such as Capacitor Energy Calculator or Parallel Capacitor Calculator.