Ah vs Wh: Understanding Battery Capacity Units
Understand the difference between Amp-hours (Ah) and Watt-hours (Wh). Learn why Wh is the universal unit for comparing batteries of different voltages.
Ah vs Wh: The Core Difference
When shopping for batteries or power banks, you'll often see capacity rated in either Amp-hours (Ah) or Watt-hours (Wh). While both are used to indicate how much charge a battery holds, they measure different things.
- Amp-hours (Ah) measures charge capacity at a specific voltage. It tells you how many amps the battery can provide for one hour.
- Watt-hours (Wh) measures total energy. Because it factors in the voltage, it represents the actual amount of work the battery can perform.
In simple terms: Ah is like the size of a fuel tank, but only if you know what kind of fuel is inside. Wh is the total amount of energy you actually get, making it the more universal unit for comparing batteries of different voltages.
Because batteries rated in different units (one manufacturer says "100Ah", another says "1200Wh") can only be fairly compared once converted to the same unit, knowing how to switch between them is essential.
Why Voltage Matters
If you have two batteries rated at 100Ah, they don't necessarily hold the same energy. A 12V 100Ah battery holds 1,200 Watt-hours of energy (12V × 100Ah = 1200Wh). A 24V 100Ah battery holds 2,400 Watt-hours of energy (24V × 100Ah = 2400Wh).
As you can see, the 24V battery holds twice the energy despite having the exact same Ah rating. This is why comparing batteries using only Amp-hours can be highly misleading unless both batteries operate at the exact same voltage.
A Worked Comparison Example
Imagine you are comparing two portable power stations. Station A claims a massive "100,000 mAh" (which is 100Ah) capacity at 3.7V. Station B claims a "500 Wh" capacity.
To compare them fairly, you must convert Station A to Watt-hours using the formula: Wh = Ah × V.
100 Ah × 3.7V = 370 Wh.
Even though "100,000 mAh" sounds larger, Station B (500 Wh) actually contains significantly more usable energy.
Which unit should you use?
For small electronics like smartphones, manufacturers still use mAh or Ah because the internal voltage (typically 3.7V for lithium-ion) is standardized and assumed. However, for solar setups, EVs, laptops, and power stations where voltages vary widely (12V, 24V, 48V, etc.), Watt-hours (Wh) or Kilowatt-hours (kWh) are the only reliable metrics for true energy capacity.