12v car battery and alternator is more than enough. The limiting factor is the fuse and/or melting wires. Thats why giant 1000w subwoofers use thick wire and larger fuses directly from the battery.
Vehicles like that will usually have an upgraded alternator, either that or be constantly dealing with a flat battery.
1kw at 12v is 85 amps, that’s well over half the capacity of a typical car alternator.
Having installed a number of systems, I think you are overestimating the care owners have for their alternator.