this is better
https://www.amazon.com/dp/B083FR3762

I don't know what kind of power consumption it needs to maintain heat as opposed to 100% load when going from cold to boiling, but finding a battery bank to run a resistive load that size is going to be more than waltzing down to the nearest Best Buy.

(warning: the below takes a lot of assumptions into play and is really just my equivalent of throwing a dart at a dartboard from about 150 meters - none of these numbers mean anything.)

Back of the napkin numbers says 1000w for 1 hour is 1kWh. Let's say it only takes a couple minutes to boil at full power, and it needs about 40% of it's full load power to maintain said heat once reached. Fudge numbers a bit, and our dartboard power requirements: 500watt-hours. For safety factor and system inefficiency (usually around 85%), plus the fact that you don't want to use more than about 60% of the battery's depth of discharge at a time, so you likely need a battery bank with around 1kWh of capacity and an inverter capable of producing 1kW of continuous power.

These do exist commercially. But you're definitely paying handsomely for that level of capacity, and most of the Chinese-produced models of these are iffy on whether or not the marketed battery capacity is even remotely obtainable, or whether the inverter circuitry can actually supply 1000w of instantaneous power without overheating the battery cells and shutting down. That's up to you to research.

hoping no one would ask because i haven't thought that through yet lol. maybe a portable power station like this but i'm open to suggestions. i'd only want to power the speakers for 1-2 hours. i'd rather not get a generator.