400Wh to Ah — 33.3 Ah at 12V
400 Wh is 33.3 Ah at 12V, 16.7 Ah at 24V, and 8.3 Ah at 48V. Below: usable energy per chemistry, what it runs, and which module count gets you there.
400 Wh at 12V is 33.3 Ah of battery capacity.
Formula: Ah = Wh ÷ V. Divide by the nominal battery voltage of the bank, not by the charger voltage.
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 | 33.3 Ah | 400 Wh | 0.4 |
| 24 V | 16.7 Ah | 400 Wh | 0.4 |
| 48 V | 8.3 Ah | 400 Wh | 0.4 |
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 % | 320 Wh | 26.7 Ah | ~3,500 |
| AGM | 50 % | 200 Wh | 16.7 Ah | ~600 |
| Gel | 50 % | 200 Wh | 16.7 Ah | ~800 |
| Flooded lead-acid | 50 % | 200 Wh | 16.7 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 | 21.3 h |
| 12V compressor fridge (average) | 45 W | 7.1 h |
| Diesel heater (fan and glow plug average) | 30 W | 10.7 h |
| Water pump (while running) | 65 W | 4.9 h |
| Laptop plus router | 75 W | 4.3 h |
| Kettle through an inverter | 1200 W | 0.3 h |
What this size is in practice
400Wh is the point where a power station can carry a 45W fridge through a night with a little margin. In battery terms it is a 33Ah 12V block - or a third of a standard 100Ah module.
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 | 33.3 Ah | 1 x 100Ah / 12V |
| 24 V | 16.7 Ah | 1 x 100Ah / 12V |
| 48 V | 8.3 Ah | 1 x 100Ah / 12V |
Other energy values (Wh)
Other capacities (Ah)
FAQ
How many Ah is 400 Wh?
400 Wh is 33.3 Ah at 12V, 16.7 Ah at 24V, and 8.3 Ah at 48V. Divide the watt-hours by the nominal battery voltage: Ah = Wh ÷ V.
How much of that 400 Wh can I use?
On LiFePO4 at 80% depth of discharge you get 320 Wh (26.7 Ah at 12V). On AGM or gel at 50% you get 200 Wh (16.7 Ah). Same nameplate, very different usable energy.
How long does that run a 12V fridge?
A compressor fridge averaging 45 W runs about 7.1 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.
What capacity is 400 Wh on a real LiFePO4 module?
At the true LiFePO4 nominal voltage of 12.8V, 400 Wh corresponds to 31.3 Ah. At a round 12V it is 33.3 Ah. Datasheets use 12.8V, most calculators use 12V.
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