How to Determine a Battery's Ampere-Hour (Ah) Capacity

To determine a battery's Ampere-Hour (Ah) capacity, we first need to know its voltage (V) and the energy it stores (Wh, Watt-Hours).

The relationship between a battery's stored energy, its voltage, and its capacity can be expressed using the following formula:

\(E = V \times Q\)

Where:

• \(E\) is the energy stored in the battery, measured in Watt-Hours (Wh);
• \(V\) is the battery's voltage, measured in Volts (V);
• \(Q\) is the battery's capacity, measured in Ampere-Hours (Ah).

Now, let's assume we have a 12V battery and we know it stores 26.4Wh of energy. To find the battery's capacity (Ah), we can substitute the known values into the formula and solve for \(Q\):

\(Q = \frac{E}{V} = \frac{26.4 \text{ Wh}}{12 \text{ V}} = 2.2 \text{ Ah}\)

So, the battery's capacity is 2.2 Ampere-Hours.

Battery Capacity Calculator — Other Battery Parameters

If you expand the "Other battery parameters" section of this battery capacity calculator, you can compute three additional parameters of a battery.

C-rate of the Battery

The C-rate is used to describe how fast a battery charges and discharges. For instance:

• A 1C battery needs one hour at 100 A to load 100 Ah.
• A 2C battery would need just half an hour to load 100 Ah.
• A 0.5C battery requires two hours to load 100 Ah.

Discharge Current

This is the current \(I\) used for either charging or discharging your battery. It is related to the C-rate by the following equation:

\(I = \text{C-rate} \times Q\)

Runtime to Full Capacity

This is simply the time \(t\) needed to fully charge or discharge the battery when using the discharge current, measured in minutes. You can calculate it using the formula:

\(t = \frac{1}{\text{C-rate}}\)