Electrically it is simple — a heating element is a steady resistive load with no starting surge — but the draw is enormous and the battery empties in minutes. The limiting factor is the battery and the cable, not the waveform or the appliance.
Heating loads are where an off-grid system meets arithmetic it cannot argue with.
The three limits it meets at once
The inverter’s continuous rating, which a heating element will approach or exceed. The battery’s maximum discharge current, set by its management system. And the cable, which has to carry that current at low voltage without dropping the voltage out from under the inverter.
Why runtime is the real answer
Divide the usable watt-hours by the appliance’s draw. For a heating appliance the result is minutes, and it is the same arithmetic whatever the battery costs. A system that boils water happily for a week is a much larger system than one that runs lights and a fridge.
What does not apply here
The waveform. A resistive element does not care whether the alternating supply is a true sine or a stepped approximation, which is why heating loads are the one place a modified sine inverter is uncontroversial.
What to check on the appliance
Its actual rating rather than its category, because appliances in the same class differ enormously. Travel appliances with lower ratings exist and they are sold for exactly this reason, taking longer to do the same job at a rate the system can sustain.
Where this page and the manufacturer’s documentation differ, the documentation is the one to follow. Every capacity, output, input window, current limit, cycle count and temperature threshold on this page comes from the maker’s own published figures, with the unit as printed and the source named. None of it is measured here, and no figure is converted into another convention, because a converted number is a different number. And for any peak figure: a surge rating means something only with the duration it can be held. A very short tolerance and a long one are printed identically. This page quotes the maker’s continuous rating as the figure to size against, reports a surge rating with its stated duration when one is published, and computes no starting current from either.
What people ask before they order
Why is a kettle worse than a fridge?
Because it converts electricity straight into heat at a very high rate. It runs briefly, but while it runs it can draw more than everything else in a van combined.
Is a gas or 12 V alternative more efficient?
A dedicated low-voltage appliance skips the inversion step, which removes one loss. Whether it suits the use is a separate question, and the maker’s own consumption figure is the one to compare.
Last reviewed 16 September 2026