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CampingCalc

Convert Ah to Wh (and back): compare battery capacity

100 Ah is not always 100 Ah: at 12.8 V the battery holds 1,280 Wh, at 24 V twice as much. Only watt-hours make batteries, power stations and power banks comparable. This converter turns Ah into Wh and back – for any nominal voltage.

Units

Enter Ah or Wh depending on the direction. mAh ÷ 1000 = Ah.

Result

Energy

1,280 Wh

100 Ah at 12.8 V

Input
1,280 Wh
Kilowatt-hours
1.28 kWh
Equals at 3.7 V
345.9 Ah
Equals at 12 V
106.7 Ah
Equals at 24 V
53.3 Ah
Show calculation
  1. 1100 Ah × 12.8 V = 1,280 Wh

 

How it's calculated

The amp-hour (Ah) describes the amount of charge, the watt-hour (Wh) the energy. The link between them is the voltage:

Wh = Ah × V Ah = Wh ÷ V
Example: 100 Ah × 12.8 V = 1,280 Wh; 1,280 Wh ÷ 24 V = 53.3 Ah

Power banks and power stations often state their capacity in mAh at 3.7 V (cell voltage): 20,000 mAh × 3.7 V = 74 Wh. At the 5 V USB output only about 12–13 Ah of that is available because of converter losses and the higher voltage.

Battery typeNominal voltage100 Ah equals
LiFePO4 (4 cells)12.8 V1,280 Wh
Lead-acid AGM/gel/flooded12.0 V1,200 Wh
LiFePO4 24 V system25.6 V2,560 Wh
Li-ion cell (power bank)3.7 V370 Wh

Worked example

A power station is rated at 1,024 Wh. How many Ah is that for a 12.8 V LiFePO4 system?

Inputs

  • Conversion: Watt-hours (Wh) → amp-hours (Ah)
  • Value: 1,024
  • Nominal voltage: 12.8 V – LiFePO4 12 V system

Result

80 Ah

Capacity

Result in Wh
1,024 Wh
Kilowatt-hours
1.024 kWh
Equals at 3.7 V
276.8 Ah
Equals at 12 V
85.3 Ah
Equals at 24 V
42.7 Ah

Calculation

  1. 1,024 Wh ÷ 12.8 V = 80 Ah

The variables explained

Ah (amp-hours)
Amount of charge: 1 Ah = 1 A of current for 1 hour.
Wh (watt-hours)
Energy: 1 Wh = 1 W of power for 1 hour. 1,000 Wh = 1 kWh.
Nominal voltage (V)
Calculation voltage of the system. LiFePO4 12 V: 12.8 V; lead-acid 12 V: 12.0 V; Li-ion cell: 3.7 V.

Common mistakes

  • Comparing batteries of different voltages in Ah – only Wh are comparable.
  • Equating a power bank's mAh with the house battery's Ah: 20,000 mAh at 3.7 V is only 74 Wh, i.e. just under 6 Ah at 12.8 V.
  • Confusing rated capacity with usable capacity: lead-acid only about 50% is usable, LiFePO4 80–90%.

Assumptions and limits

  • The conversion uses the nominal voltage; the real voltage varies with state of charge and load, which doesn't change the energy content.