How long will a 100Ah battery run a 12V fridge?
By Sithum Imarsha Last reviewed
A Dometic CFX5 45 uses 0.76 Ah an hour at 32 °C. 100Ah of LiFePO4 at 80% usable runs it for about 4.4 days with no charging. 100Ah of lead-acid at 50% runs it for about 2.7 days.
Your result
Runtime
4.4 days
1,024 Wh usable ÷ 9.7 W at the battery = 105.3 h
- Usable energy
- 1,024Wh
- At the battery
- 9.7W
- Battery current
- 0.8A
- C-rate
- 0.01C
- Without idle draw
- h
- Common shortcut
- 131.6h
The shortcut: volts × Ah ÷ watts, all of the battery, no inverter. It is what many tools show.
Choosing an inverter? Check its size and the current it pulls.
Fix the highlighted field to update.
How we calculated this
- Usable energy is the battery volts times its amp hours, times the share you can safely use.
- A mains load runs through an inverter, so its losses and idle draw are added.
- Runtime is the usable energy divided by the power drawn at the battery. Lead-acid loses capacity at high current.
Usable energy
12.8 V × 100 Ah × 80% = 1,024 Wh
Power at the battery
9.12 W ÷ 12 V = 0.76 A, × 12.8 V = 9.7 W
Runtime
1,024 Wh ÷ 9.7 W = 105.3 h
Current and rate effect
0.8 A, 0.01C, 100% of rated capacity
| Battery | Usable Wh | Hours |
|---|---|---|
| LiFePO4 (lithium) | 1,024 | 105.3 |
| Lead-acid (AGM, gel or flooded) | 600 | 65.8 |
| Shortcut: volts × Ah, all of it, no inverter | 1,200 | 131.6 |
Each type at its default usable share and rate effect, same capacity, load and inverter. The shortcut row is what you get from volts × Ah ÷ watts.
This version starts with a 100 Ah LiFePO4 battery running a 12 V compressor fridge straight from the battery (DC, no inverter): a Dometic CFX5 45 at 0.76 Ah an hour, which is 9.12 W at 12 V. The table under the working compares lead-acid.
100Ah battery and 12V fridge: what the sources say
Official source
- Dometic rates the CFX5 45 (46 L) at 0.76 Ah an hour at 12 V, with 32 °C outside and 4 °C inside. In cooler weather it uses less.
- Victron battery monitors use 50% as the default discharge floor for lead-acid. Two lithium makers rate cycle life at 80% depth of discharge. We use the same.
Estimate
- On the same battery, an 80 W TV through a small inverter lasts about 10.8 hours. The inverter and the TV draw far more than the fridge's average.
New to battery maths? Read how runtime is worked out on the main battery runtime calculator.
Questions
How many watt hours is a 100Ah battery?
A 12.8 V LiFePO4 battery holds 12.8 × 100 = 1,280 Wh. A 12 V lead-acid battery holds 1,200 Wh. You can use about 80% of the lithium and 50% of the lead-acid.
Why does the fridge not run all the time?
Its compressor switches on and off. Dometic's 0.76 Ah an hour is the average, so you do not need a duty cycle. The rated input of 9.4 A is the most it draws, not its average.
Can a 100Ah battery run a 1,000 W inverter?
At full load a Victron Phoenix 1200 VA (1,000 W) pulls about 87 A from a 12.8 V battery. That is under a 100 A limit, but close. A 2,000 W load pulls about 169 A.