120Ah to Wh — 1,440 Wh at 12V
120Ah stores 1,440 Wh at 12V, 2,880 Wh at 24V, and 5,760 Wh at 48V. Below: usable energy per chemistry, what it runs, and how the same energy is built from standard modules.
120Ah at 12V is 1,440 Wh — that is 1.44 kWh of nameplate energy.
Formula: Wh = Ah × V. The voltage is the nominal battery voltage, not the charging voltage.
A real LiFePO4 module of 120Ah is usually labelled 1,536 Wh, because its nominal voltage is 12.8V rather than a round 12V. Both 1,440 Wh and 1,536 Wh describe the same battery.
Result
Energy in Wh equals capacity in Ah multiplied by battery voltage. 1000 Wh equals 1 kWh.
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Design Your SystemAt every system voltage
The same capacity stores four times the energy at 48V that it does at 12V, and draws a quarter of the current for the same load.
| System voltage | Capacity | Energy | kWh |
|---|---|---|---|
| 12 V | 120 Ah | 1,440 Wh | 1.44 |
| 24 V | 120 Ah | 2,880 Wh | 2.88 |
| 48 V | 120 Ah | 5,760 Wh | 5.76 |
How much of it you can actually use
Nameplate energy is not usable energy. Depth of discharge caps what you may take out before you damage the battery, and it differs by chemistry.
| Chemistry | Depth of discharge | Usable energy | Usable capacity | Cycles at that DoD |
|---|---|---|---|---|
| LiFePO4 | 80 % | 1,152 Wh | 96 Ah | ~3,500 |
| AGM | 50 % | 720 Wh | 60 Ah | ~600 |
| Gel | 50 % | 720 Wh | 60 Ah | ~800 |
| Flooded lead-acid | 50 % | 720 Wh | 60 Ah | ~400 |
What that runs
Runtime from the usable LiFePO4 energy at 12V (80% depth of discharge), one load at a time, no inverter losses on the DC rows.
| Load | Power | Runtime |
|---|---|---|
| LED lighting | 15 W | 76.8 h |
| 12V compressor fridge (average) | 45 W | 25.6 h |
| Diesel heater (fan and glow plug average) | 30 W | 38.4 h |
| Water pump (while running) | 65 W | 17.7 h |
| Laptop plus router | 75 W | 15.4 h |
| Kettle through an inverter | 1200 W | 1 h |
What this size is in practice
120Ah is a common OEM motorhome size - the AGM or gel block many European converters fit at the factory, often under the driver seat. It is the usual starting point for a "swap to lithium without changing the compartment" question.
Building the same energy from standard modules
How many standard 100Ah 12V modules add up to this energy, and what capacity that becomes at each system voltage.
| System voltage | Capacity | Standard modules |
|---|---|---|
| 12 V | 120 Ah | 1 x 100Ah / 12V |
| 24 V | 60 Ah | 1 x 100Ah / 12V |
| 48 V | 30 Ah | 1 x 100Ah / 12V |
Other capacities (Ah)
Other energy values (Wh)
FAQ
How many Wh is 120Ah?
120Ah is 1,440 Wh at 12V, 2,880 Wh at 24V, and 5,760 Wh at 48V. Multiply the amp-hours by the nominal battery voltage: Wh = Ah × V.
How much of that 1,440 Wh can I use?
On LiFePO4 at 80% depth of discharge you get 1,152 Wh (96 Ah at 12V). On AGM or gel at 50% you get 720 Wh (60 Ah). Same nameplate, very different usable energy.
How long does that run a 12V fridge?
A compressor fridge averaging 45 W runs about 25.6 hours on the usable LiFePO4 energy at 12V. Cycling depends on ambient temperature, so treat this as the upper bound for a well-insulated unit.
Why does the datasheet say 1,536 Wh instead of 1,440 Wh?
Because LiFePO4 has a nominal voltage of 12.8V per 12V module, not exactly 12V. 120Ah × 12.8V = 1,536 Wh. The 12V figure of 1,440 Wh is the conservative system-voltage calculation. Both describe the same battery.
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