What Is Battery Capacity (Ah) and How Does It Relate to Energy (Wh)?

When you read a battery datasheet you meet two numbers everywhere: Ah (ampere-hour) and Wh (watt-hour). They are often confused, but they measure two different things.

Capacity (Ah) = the amount of charge

Capacity describes how much electric charge a battery can store and deliver. One ampere-hour means the battery can supply 1 ampere of current for 1 hour — or 2 A for half an hour, and so on. It says nothing yet about voltage, only about the quantity of charge.

Energy (Wh) = the actual usable energy

Energy describes how much work that charge can do. It is the product of capacity and voltage:

A 100Ah battery at 48V stores 100 × 48 = 4800Wh = 4.8kWh. The same 100Ah at 12V would store only 1.2kWh.

Why the distinction matters

• Two batteries with the same Ah but different voltages hold very different energy — always compare in kWh, not Ah.
• Residential systems are commonly quoted in kWh (usable energy); cells and modules are quoted in Ah (raw capacity).
• Module/cell configuration (series × parallel) turns Ah into total system voltage and energy.

In short: Ah tells you the size of the tank, Wh tells you the fuel it carries.