A DC air conditioner only cools for as long as the battery bank behind it lasts. The good news with Nomadic Cooling is that Nomadic publishes averaged watt and amp figures for each model and mode, measured across 70 to 100+°F test ranges, so you can do the math before you buy. This guide turns those figures into runtime tables for the X2 Helix Gen II, X3 Helix and S1 Helix on 12V and 48V lithium banks, then shows what it takes to get through an eight-hour night.
How we did the math
- Usable battery energy (LiFePO4): amp-hours x 12.8 V x 90% on a 12V bank, or amp-hours x 51.2 V x 90% on a 48V bank. The 90% leaves a small reserve.
- Runtime: usable watt-hours divided by the air conditioner's average watts.
- Duty cycle: we assume the unit runs at Nomadic's average draw for that mode the whole time. On a cool night, or once the cabin is down to temperature, a PWM compressor often ramps lower, so real runtime can be longer. On a hot, sunny day with poor insulation it can be shorter.
- No charging and no other loads: the tables leave out solar, alternator and shore power, and leave out the fridge, fans and lights. Subtract those yourself, or use our solar and battery calculator.
Why watts and not amps? Nomadic's watt and amp figures divide out to about 14.7 V on the 12V models, which looks like a charging-level test voltage. A LiFePO4 bank resting near 12.8 V delivers the same watts at a higher current, so working in watts gives a more conservative and more honest answer.
Nomadic's average draw by model and mode
| Model and mode | 12V average | 48V average |
|---|---|---|
| X2 Helix Gen II, ECO | ~526 W | ~452 W |
| X2 Helix Gen II, Full AC | ~871 W | ~913 W |
| X3 Helix, ECO (provisional) | ~899 W | ~523 W |
| X3 Helix, Full AC (provisional) | ~1,297 W | ~1,386 W |
| S1 Helix, ECO (planning) | ~486 W | ~451 W |
| S1 Helix, Full AC (planning) | ~879 W | ~948 W |
X2 figures are Nomadic's planning averages for the current X2 Helix platform. X3 figures are provisional and S1 figures are planning estimates, both pending certification, so treat them as planning values.
Runtime on a 12V lithium bank
| 12V LiFePO4 bank (usable Wh) | X2 ECO | X2 Full | X3 ECO | X3 Full | S1 ECO | S1 Full |
|---|---|---|---|---|---|---|
| 200 Ah (2,304 Wh) | 4.4 h | 2.6 h | 2.6 h | 1.8 h | 4.7 h | 2.6 h |
| 300 Ah (3,456 Wh) | 6.6 h | 4.0 h | 3.8 h | 2.7 h | 7.1 h | 3.9 h |
| 400 Ah (4,608 Wh) | 8.8 h | 5.3 h | 5.1 h | 3.6 h | 9.5 h | 5.2 h |
| 600 Ah (6,912 Wh) | 13.1 h | 7.9 h | 7.7 h | 5.3 h | 14.2 h | 7.9 h |
| 800 Ah (9,216 Wh) | 17.5 h | 10.6 h | 10.2 h | 7.1 h | 19.0 h | 10.5 h |
Runtime on a 48V lithium bank
| 48V LiFePO4 bank (usable Wh) | X2 ECO | X2 Full | X3 ECO | X3 Full | S1 ECO | S1 Full |
|---|---|---|---|---|---|---|
| 100 Ah (4,608 Wh) | 10.2 h | 5.0 h | 8.8 h | 3.3 h | 10.2 h | 4.9 h |
| 200 Ah (9,216 Wh) | 20.4 h | 10.1 h | 17.6 h | 6.6 h | 20.4 h | 9.7 h |
| 300 Ah (13,824 Wh) | 30.6 h | 15.1 h | 26.4 h | 10.0 h | 30.7 h | 14.6 h |
A 100 Ah 48V bank stores the same energy as a 400 Ah 12V bank (both 4,608 Wh usable here). Runtimes differ between the two tables because Nomadic's figures for each voltage version are different, not because 48V stores more.
What an eight-hour night takes
Eight hours is the number most owners ask about. Multiply the average watts by eight, then divide by the usable volts per amp-hour (11.52 on 12V, 46.08 on 48V):
| Model and mode | Energy for 8 h | 12V bank needed | 48V bank needed |
|---|---|---|---|
| X2 ECO | 4,208 Wh (12V) / 3,616 Wh (48V) | about 365 Ah | about 78 Ah |
| X2 Full AC | 6,968 Wh / 7,304 Wh | about 605 Ah | about 159 Ah |
| X3 ECO (provisional) | 7,195 Wh / 4,184 Wh | about 625 Ah | about 91 Ah |
| X3 Full AC (provisional) | 10,378 Wh / 11,088 Wh | about 901 Ah | about 241 Ah |
| S1 ECO (planning) | 3,888 Wh / 3,608 Wh | about 338 Ah | about 78 Ah |
| S1 Full AC (planning) | 7,032 Wh / 7,584 Wh | about 610 Ah | about 165 Ah |
Those are the bare minimums for the air conditioner alone, running non-stop at its average. Nomadic's own advice is to plan with margin and not build a power system around the exact minimum. Add the fridge, fans and lights, then round up. In practice that points most 12V X2 and S1 owners toward a 400 to 600 Ah bank for an ECO night, and pushes the X3 on 12V into the 600 Ah and up range.
Where solar fits
Nomadic describes solar as a runtime extender, not a promise that the air conditioner will run indefinitely. To put back the energy an eight-hour ECO night uses, you need the daily watt-hours divided by about 4 to 5 sun hours and a 75% real-world factor:
- X2 ECO on 12V (4,208 Wh): about 1,120 to 1,400 W of panels.
- S1 ECO on 12V (3,888 Wh): about 1,040 to 1,300 W of panels.
- X3 ECO on 48V (4,184 Wh, provisional): about 1,120 to 1,400 W of panels.
That is a lot of roof, which is why the X2's compact footprint and the S1's roof-free layout matter. At 12V, an array that size also needs more than one charge controller in the 50 A class; a Victron SmartSolar MPPT 100/50, for example, uses at most about 700 W of panel at 12V. Charging from the alternator while driving and from shore power when you have it closes the rest of the gap.
Ways to stretch the runtime
- Use ECO overnight. On the X2 12V, ECO averages about 526 W against about 871 W on Full AC.
- Pre-cool while the alternator or shore power is still connected, then let ECO hold the temperature. Nomadic's X3 page suggests a "Quiet Night" scene in Helix to hold comfort at lower compressor speeds.
- Cover windows with reflective shades, park in shade and keep airflow paths clear. Nomadic lists all of these.
- Set a realistic target temperature. A few degrees warmer makes a measurable difference on a hot night.
Questions
Can a 200 Ah 12V battery run a Nomadic air conditioner overnight?
Not for a full night. At Nomadic's averages a 200 Ah 12V LiFePO4 bank gives about 4.4 hours of the X2 on ECO and about 4.7 hours of the S1 on ECO, before any other loads.
Is 48V better for battery runtime?
Not by itself. Runtime depends on stored energy (watt-hours), not voltage. 48V helps because the current drops to roughly a third or less of the 12V figure (about 17.7 A against 59 A for the X2 on Full AC), which means smaller cable, less voltage drop and less heat. See our 12V vs 48V guide.
How is this different from running a 120V roof air conditioner on batteries?
A 120V rooftop unit has to go through an inverter, and starting surge and inverter losses add to the load. Our answer on whether lithium can run a roof air conditioner for 8 hours covers that case. A DC unit like Nomadic's skips the inverter.
Which batteries do you carry?
See our lithium LiFePO4 batteries, and the full Nomadic Cooling range. Everything ships from our warehouse in Upland, California. Send us your model, bank size and how many hours you need and we will check the numbers with you.