Huge capacitors can store a lot of power and deliver it instantly, but that power has to come from someplace…The extra “Boost” battery can be wired to the existing alternator, but it will be over-worked and prone to premature failure…If the TIME the Big Sound system is cranked up is limited, say to 20% of the cars on time, then the 70 amp alternator should be able to keep up during the “rest” periods…