400Ah to Wh — 4,800 Wh at 12V
400Ah stores 4,800 Wh at 12V, 9,600 Wh at 24V, and 19,200 Wh at 48V. Below: usable energy per chemistry, what it runs, and how the same energy is built from standard modules.
400Ah at 12V is 4,800 Wh — that is 4.8 kWh of nameplate energy.
Formula: Wh = Ah × V. The voltage is the nominal battery voltage, not the charging voltage.
A real LiFePO4 module of 400Ah is usually labelled 5,120 Wh, because its nominal voltage is 12.8V rather than a round 12V. Both 4,800 Wh and 5,120 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 | 400 Ah | 4,800 Wh | 4.8 |
| 24 V | 400 Ah | 9,600 Wh | 9.6 |
| 48 V | 400 Ah | 19,200 Wh | 19.2 |
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 % | 3,840 Wh | 320 Ah | ~3,500 |
| AGM | 50 % | 2,400 Wh | 200 Ah | ~600 |
| Gel | 50 % | 2,400 Wh | 200 Ah | ~800 |
| Flooded lead-acid | 50 % | 2,400 Wh | 200 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 | 256 h |
| 12V compressor fridge (average) | 45 W | 85.3 h |
| Diesel heater (fan and glow plug average) | 30 W | 128 h |
| Water pump (while running) | 65 W | 59.1 h |
| Laptop plus router | 75 W | 51.2 h |
| Kettle through an inverter | 1200 W | 3.2 h |
What this size is in practice
400Ah is bank territory: four 100Ah modules, or four large prismatic cells at 48V. At this size the system voltage decision matters more than the capacity itself - the same 400Ah is 4.8kWh at 12V and 19.2kWh at 48V, and the DC current differs by a factor of four.
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 | 400 Ah | 4 x 100Ah / 12V |
| 24 V | 200 Ah | 4 x 100Ah / 12V |
| 48 V | 100 Ah | 4 x 100Ah / 12V |
Other capacities (Ah)
Other energy values (Wh)
FAQ
How many Wh is 400Ah?
400Ah is 4,800 Wh at 12V, 9,600 Wh at 24V, and 19,200 Wh at 48V. Multiply the amp-hours by the nominal battery voltage: Wh = Ah × V.
How much of that 4,800 Wh can I use?
On LiFePO4 at 80% depth of discharge you get 3,840 Wh (320 Ah at 12V). On AGM or gel at 50% you get 2,400 Wh (200 Ah). Same nameplate, very different usable energy.
How long does that run a 12V fridge?
A compressor fridge averaging 45 W runs about 85.3 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 5,120 Wh instead of 4,800 Wh?
Because LiFePO4 has a nominal voltage of 12.8V per 12V module, not exactly 12V. 400Ah × 12.8V = 5,120 Wh. The 12V figure of 4,800 Wh is the conservative system-voltage calculation. Both describe the same battery.
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