If your audio system constantly draws more amperage than your alt produces, it will drain your battery, to the point of the battery needing to be recharged by something like a trickle or like deep cycle charger, whatever. The alt isn’t really going to recharge batteries that well, at least, not when they’re deeply drained. You can measure the resting voltage of your battery after a charge and see after how much it’s resting at to see how much stress the battery is under after you play the system for a while. Batteries are really mostly there like slow moving capacitors, optimally, where high peak amperage draw can be buffered or load-dampened by the batteries to lessen current-draw stress on the alt, but that’s only while the vehicle is on, I mean. Some newer batteries are much, much better than the typical sealed agm type batteries.
If you draw more amperage than your alt produces, then it’s going to run your batteries down, usually. The alt is the only thing that actually produces power; everything else just stores it.
Amp Hours is the measurement, where how many amps your system draws can be timed to how fast it drains the battery, roughly, with no alt charging, but you’d have to know your system amperage draw somehow.