How to Convert Amp-Hours (Ah) to Watt-Hours (Wh)

Watt-hours = Amp-hours × Voltage. A 100Ah battery at 12V stores 1,200Wh (100 × 12). At 24V, that same 100Ah rating stores 2,400Wh, and at 48V it stores 4,800Wh — the amp-hour number alone tells you nothing about actual energy storage until you multiply it by voltage.

This is the single most useful formula in the entire off-grid and backup-power world, because it’s the only way to fairly compare batteries, power stations, and solar setups that use different voltage systems.

The Formula

Wh = Ah × V

That’s it. Three numbers, one multiplication. The part that trips people up isn’t the math — it’s remembering that Ah by itself is meaningless without knowing the voltage it’s rated at.

Why Amp-Hours Alone Are Misleading

Amp-hours measure electrical charge — literally how many amps the battery can deliver for how many hours. But charge isn’t energy. A 100Ah battery at 12V and a 100Ah battery at 24V hold the same “amount” of charge on paper, but the 24V battery actually stores twice the usable energy, because energy also depends on the pressure (voltage) pushing that charge through a circuit. This is exactly why you can’t compare two batteries’ capacity fairly by Ah rating alone unless they’re at the same voltage — you have to convert to Wh first.

Worked Examples

Notice the fourth and fifth rows: both are rated “100Ah,” but they store dramatically different amounts of usable energy because the voltage is different. If you were comparing battery listings by Ah rating alone, you’d badly misjudge which one actually gives you more runtime.

Going the Other Direction: Wh to Ah

Sometimes you’ll have a device’s Wh rating (common on portable power stations) and need to know its equivalent Ah at a specific voltage — useful when matching accessories or comparing to a traditional 12V battery bank.

Ah = Wh ÷ V

For a 1,000Wh power station’s internal battery expressed at 12V: 1,000 ÷ 12 ≈ 83Ah. Keep in mind many power stations actually run their internal cells at a different voltage than their output, so this is a useful approximation for comparison purposes, not necessarily the literal internal battery spec.

Where This Conversion Actually Matters

• Comparing a power station (rated in Wh) to a traditional deep-cycle or lithium battery (rated in Ah). You can’t compare them directly until you convert one to match the other’s unit.
• Sizing a solar or generator charging setup. Charging calculations (how many panel-watts, how many charging amps) are far easier to reason about once everything is in consistent units.
• Comparing batteries at different system voltages — a common point of confusion when researching 12V vs. 24V vs. 48V system designs, since the “bigger Ah number” isn’t automatically the bigger battery.
• Estimating runtime for a specific appliance. Once you know a battery’s Wh capacity, you can divide by an appliance’s wattage to estimate hours of runtime (accounting for inverter efficiency losses, typically 10–15%).

A Quick Sanity Check Method

If a number seems off, plug it back into the formula and check whether it makes physical sense: a battery advertised as “1,200Wh” at 12V should show roughly 100Ah (1,200 ÷ 12 = 100) — if the listed Ah doesn’t roughly match, double check the voltage being used, since some manufacturers list nominal voltage while others use a slightly different rated voltage, which can shift the numbers by a small margin.

Frequently Asked Questions

Does this formula work for AC power too, or only DC batteries? The same Wh = Ah × V relationship applies to any voltage and current combination, DC or AC, though for AC circuits with reactive loads (like motors), a related but slightly different figure called VA (volt-amps) sometimes comes into play. For batteries and most DC solar/off-grid calculations, the straightforward Wh = Ah × V formula is accurate.

Why do some battery labels list Ah and others list Wh? Traditional lead-acid and many standalone lithium batteries have historically been rated in Ah, a holdover from older battery industry convention. Portable power stations, being marketed to a broader consumer audience unfamiliar with voltage systems, generally use Wh instead, since it’s a single number that already accounts for voltage and is easier to compare across products.

Is a higher voltage battery always “better” for the same Ah rating? Not automatically “better” — just different, and appropriate for different systems. A higher-voltage battery at the same Ah rating stores more total energy, but your other components (inverter, wiring, appliances) need to be rated for that voltage too. Don’t chase a higher-voltage battery without designing your whole system around it.

How do I find my battery’s actual voltage if it’s not clearly labeled? Check the manufacturer’s spec sheet, or measure it directly with a multimeter across the battery’s terminals — a “12V” battery will typically read somewhere around 12.6–13.6V at rest depending on charge level and chemistry.