# Battery size calculator

The battery size calculator calculates the battery size in ampere-hour (Ah).

## See Also

## Parameters

**Load type (ampere or watt):**Select the unit in which the load will be specified, ampere or watt.**Load (watt)**: If the load type is watt, specify the load in watt, for example 100 W. Use and average value if its a cyclical load.**Load (ampere):**If the load type is ampere, specify the current in ampere, for example 10 A.**Voltage (V**: Specify the battery voltage in volts DC, if the load type is watt._{dc})**Required duration (hours):**Specify the duration that the load must be supplied for.**Battery type:**Select the battery type. Lead-acid or lithium-ion.**Remaining charge (%):**Specify the required remaining charged. To prolong the life of a battery, a lead-acid battery should not frequently be discharged below 50 %, and Lithium-ion battery not below 20%. Note that 0% is a flat battery and 100% if a full battery.

## How to calculate battery current?

If the load is specified in watt, the current **I** is calculated as:

\(I=\dfrac{P}{V_{dc}}\)

Where:

**P**is the power in watts.

**V**is the voltage in volts DC.

_{dc}## How to calculate the battery size for a Lithium-ion battery?

The required battery size \(B_{li-ion}\) for litium-ion batteries is calculated as:

\(B_{li-ion}=\dfrac {100 \cdot I \cdot t}{100 – Q}\)

Where:

**I**is current in ampere.**t**is the duration in hours.**Q**is the required remaining charge in percentage.

## How to calculate the battery size for a Lead-acid battery?

The required battery size \(B_{lead-acid}\) for lead-acid batteries is calculated as:

\(B_{lead-acid}=\dfrac{100 \cdot I \cdot t}{(100-Q) \cdot (0.02 \cdot t+0.6)}\)

Where:

**I**is current in ampere.**t**is the duration in hours.**Q**is the required remaining charge in percentage (%).

The battery rating of a lead-acid batteries is proportional to the discharge rate.

They are typically rated for a discharge rate over 20 hours.

For example, a 20 Ah battery can deliver 1 A for 20 hours, which amounts to 20 Ah.

The rating of the battery reduces by approximately 62% if it is discharged in 1 hour.

For example, if the same 20 Ah battery is discharged in one hour, it can only deliver 12.4 A for one hour, which amounts to 12.4 Ah.

The battery size calculator derates the battery linearly based in this characteristic.