amplifier are of many types
we use POWER AMPLIFIER to run woofer
it all depends how much your amplifier gives power
agar small amplfier hai , by mean of giving low power , no need to change battery
similarly amplifier gives much power ,to subwoofer
it requires Bigger battery , or additional battery
Beside there is a source to provide power to battery (for charging)
called dynamo or alternator , which is also replaced by Heavy Amphere Alternator
OHM LAW formulae rules over their
if you are running system on 40A batter
and you change you battery from 40A to 120A
then you can run 3 times more time duration