Ah vs Wh: what's the difference?

In Ah vs Wh, amp hours (Ah) measure how much charge a battery holds, while watt hours (Wh) measure how much energy it holds. The difference is voltage: Wh = Ah x volts. This matters because two batteries with the same Ah can store completely different amounts of energy if their voltages differ. A 12V 100Ah battery holds 1,200Wh, but a 24V 100Ah battery holds 2,400Wh, twice the energy from the same Ah figure. So comparing batteries on Ah alone, without voltage, is the single most common mistake buyers make.

Most pages define the two units and stop. The point that actually changes decisions is that Ah is voltage-blind, so it is only meaningful within one voltage. Wh is the honest cross-comparison number. This guide separates the two clearly.

Ah vs Wh at a glance

Sources: RELiON, Rebel Cell, BSLBATT, LiTime, LiFePO4 Battery Shop (2023–2026). Verify at publish.

What amp hours (Ah) actually measure

Amp hours measure charge: how many amps a battery can supply for how long. A 150Ah battery can, in theory, deliver 150A for one hour, or 75A for two hours. It tells you nothing about energy on its own, because it ignores voltage. That is why Ah is only a fair comparison between batteries of the same voltage. Ah does, however, decide something Wh does not: current sizing. Wire gauge and fuse ratings are set by amps, not watt hours, so the Ah/current side matters for safe wiring.

What battery watt hours (Wh) measure

Battery watt hours measure total energy, folding voltage and charge into one number. Wh = Ah x V. A 12V 100Ah battery stores 12 x 100 = 1,200Wh. A 24V 50Ah battery also stores 24 x 50 = 1,200Wh, the same energy, in roughly the same size and weight, just at a different voltage. Because Wh includes voltage, it is the correct unit for comparing batteries of different voltages and for matching a battery to an appliance's wattage.

Amp hour calculation and Wh conversion (the math)

Here is the amp hour calculation both ways, with worked numbers.

A practical runtime example: a 1,200Wh battery running a 600W appliance lasts about 1,200 / 600 = 2 hours (before efficiency and depth-of-discharge losses). The same works via Ah: a 12V 100Ah battery running a 15A load lasts 100 / 15 = about 6.7 hours. Both routes give the same answer because W = V x A.

Why series and parallel change Ah but not always Wh

This is where Ah confuses people. Connect two 12V 100Ah batteries in series and you get 24V 100Ah: the Ah stays 100, but the energy doubles to 2,400Wh because voltage doubled. Connect them in parallel and you get 12V 200Ah: the Ah doubles to 200, and energy also doubles to 2,400Wh. Either way the Wh is the same, which is exactly why Wh is the reliable figure and Ah alone can mislead. This wiring logic is the same one used for sizing larger banks in the 3kVA inverter battery guide.

The usable-energy caveat competitors skip

Even Wh is not the full story, because you cannot use all of it. Lead-acid is safely used to about 50% depth of discharge, lithium to 80 to 90%. So a 1,200Wh lead-acid battery gives roughly 600Wh usable, while a 1,200Wh lithium gives around 1,020Wh usable. When you compare batteries, compare usable Wh, not rated Wh. This ties directly to the chemistry differences in lead acid vs lithium battery, and to sizing in the inverter battery capacity guide.

Honest pros and cons of each unit

Ah is simple and directly sizes wiring and fusing, but it is voltage-blind and misleads across different voltages. Wh is the honest energy figure for cross-comparison and runtime, but you still must apply depth of discharge to get usable energy. Use Ah within one voltage, Wh across voltages.

Which unit should you use?

• Use Ah when: comparing batteries at the same voltage, or sizing cables and fuses (which depend on current).
• Use Wh when: comparing batteries at different voltages, or matching a battery to an appliance's wattage and runtime.
• Use usable Wh when: making the real buying decision, after applying depth of discharge for the chemistry.
• Not a fair comparison: judging two different-voltage batteries on Ah alone.

FAQs

What is the difference between Ah and Wh?

Amp hours (Ah) measure charge; watt hours (Wh) measure energy. Wh includes voltage (Wh = Ah x V), so Wh compares batteries across different voltages while Ah only compares fairly at the same voltage.

How do I convert Ah to Wh?

Multiply amp hours by voltage: Wh = Ah x V. A 12V 100Ah battery holds 1,200Wh. To go the other way, divide: Ah = Wh / V.

Can two batteries have the same Ah but different energy?

Yes. A 12V 100Ah battery holds 1,200Wh, but a 24V 100Ah battery holds 2,400Wh. Same Ah, double the energy, because voltage differs. This is why Ah alone can mislead.

What is the amp hour calculation for runtime?

Divide battery Ah by the load current in amps. A 100Ah battery at a 15A draw lasts about 6.7 hours, before efficiency and depth-of-discharge losses. In Wh terms, divide battery Wh by the appliance wattage.

Why do we measure battery watt hours instead of just Ah?

Because battery watt hours include voltage, giving total energy in one number. This lets you compare batteries of different voltages and match them to appliance wattage, which Ah alone cannot do.

Does connecting batteries in series or parallel change Ah or Wh?

Series doubles voltage and keeps Ah the same; parallel doubles Ah and keeps voltage the same. Either way the total Wh is the same, which is why Wh is the reliable comparison figure.

How much of a battery's Wh can I actually use?

About 50% for lead-acid and 80 to 90% for lithium, to protect battery life. Always compare usable Wh, not rated Wh, when choosing a battery.

Which unit should I use to size a battery for my home?

Work in Wh: add up appliance wattages times hours to get daily Wh, add 10 to 20% for inverter losses, then divide by usable depth of discharge. Convert to Ah only after picking your system voltage.