Batteries

Ah vs Wh vs kWh

Amp-hours only mean something if you also know the voltage. That single omission is why battery comparisons go wrong.

Published 23 August 2026 · Published by SnapEnergyLab. Methodology and default assumptions are documented separately.

A single lithium cell, a prismatic battery block and a large battery module lined up on a bright studio surface at very different scales

Quick answer

Amp-hours measure charge, not energy. Two batteries can both be “100 Ah” and differ fourfold in the energy they hold, because energy is charge multiplied by voltage.

Watt-hours and kilowatt-hours are energy, and they are directly comparable across any voltage or chemistry. When you are comparing products, convert everything to Wh or kWh first — then compare.

How to read the numbersYour inputCalculated result

Capacity: 100 Ah; Your input
Nominal voltage: 51.2 V; Your input
Stored energy: 5.12 kWh; Calculated result

The conversions

Wh = Ah × nominal voltage (V)
kWh = Wh ÷ 1000 = Ah × V ÷ 1000
Ah = Wh ÷ V = kWh × 1000 ÷ V
Ah = mAh ÷ 1000

Always use the battery's nominal voltage, not the fully charged voltage. A 51.2 V LFP rack sits near 57 V at full charge; using that inflates the energy figure by about 11%.

Why amp-hours mislead

Charge is how many electrons moved; energy is how much work they can do. Voltage is the difference. Raising the voltage of a pack while keeping its amp-hours the same multiplies its energy, which is exactly why the storage industry moved from 12 V to 48 V and why EVs run at 400–800 V.

It also explains a common shopping mistake: a 100 Ah 12 V battery advertised alongside a 100 Ah 48 V battery at four times the price is not overpriced. It holds four times the energy.

Charge capacity, nominal voltage and stored energy for common battery formats
Format	Charge capacity	Nominal voltage	Stored energy
Power bank	20,000 mAh	3.7 V	74 Wh
12 V leisure battery	100 Ah	12.8 V	1,280 Wh (1.28 kWh)
24 V bank	100 Ah	25.6 V	2,560 Wh (2.56 kWh)
48 V rack battery	100 Ah	51.2 V	5,120 Wh (5.12 kWh)
EV traction pack	120 Ah	400 V	48,000 Wh (48 kWh)

Worked example: sizing a 48 V bank from an energy target

Energy needed at the DC bus9.0 kWhYour input
System nominal voltage51.2 VYour input
Charge capacity required9,000 ÷ 51.2 = 175.8 AhCalculated result
Depth of discharge allowed90%Site default
Nominal capacity required175.8 ÷ 0.90 = 195.3 AhCalculated result

Specify at least200 Ah at 51.2 V (10.24 kWh)

One more number: C-rate

Capacity tells you how much energy is stored; C-rate tells you how quickly you may take it out. A 100 Ah battery rated 1C can supply 100 A continuously; at 0.5C it can supply 50 A. Multiply the current limit by the nominal voltage to get the power limit in watts — 100 A at 51.2 V is 5.1 kW.

Two packs with identical kWh figures and different C-ratings behave completely differently in a backup role. Energy determines how long; C-rate and the inverter determine what you can switch on.

Convert between Ah and kWh directly

Enter amp-hours and nominal voltage for the stored energy, or work the other way with the kWh to Ah converter. Both show the exact arithmetic rather than a rounded result.

Open the Ah to kWh converter

Assumptions and limitations

Nominal voltages in the table are conventional values for common chemistries; your battery's datasheet is authoritative.
Stored energy is not deliverable energy. Depth of discharge, conversion efficiency, temperature and age all reduce what reaches a load.
Charge capacity itself varies with discharge rate: a battery discharged rapidly delivers fewer amp-hours than the same battery discharged slowly.

Sources

The International System of Units (SI), 9th edition — BIPM
Supports: Definitions of the ampere, volt, watt and their derived energy units.
IEC 62620 — Secondary lithium cells and batteries — International Electrotechnical Commission
Supports: Rated capacity is declared with a nominal voltage; capacity in Ah is only comparable at equal voltage.