Pick your radio, tell it how much you'll be talking, and get either how long a battery will last or what size battery to buy. Built for field days, POTA, nets, and grid-down planning.
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Choose a preset or pick Custom. Preset numbers are typical manufacturer specs — check your manual if you want exact figures.
Most radios turn roughly a third of their DC input into RF, so 100 W out pulls about 20–23 A at 13.8 V. 35% is a safe default.
How much of the time you're keyed up, listening to traffic, or sitting squelched. Pick a style to fill these in, then adjust.
Laptop for FT8, antenna tuner, lights, phone charger, fan — anything else pulling from this battery.
Battery type matters — lead-acid batteries shouldn't be drained much past half, lithium can use almost all of it.
Safety margin covers battery aging, wiring loss, and the plan going longer than expected. 20% is a good default.
Want a radio added to the preset list? Send it over.