Casablanca Car

hi i have one mono amplifier
320 rms watts per channel x 1@4ohm <1%thd+n
s/n:>80dba{reference 1 walt into 4 ohm}
500 total rms watts @ 2ohm <1% thd+n all

(L) 16.65 (W) 7.675 (H) 2.4

and i have one 10 inch subwoofer 300 watts and one 12 inch subwoofer and this is what it says on the back of the 12 inch (impedance:2ohm+2ohm frequency responce:20Hz-300Hz rated power 150 watts max.input power 450 watts.

so i put it them both in my car but after a while of having the music to loud with bass the same song starts to skip i dont know if is my amplifier that cant handle the 10 inch and the 12 inch together or maybe is my car battery thank you.
the car is a 1991 toyota corolla and a friend made me a custom box to put the 10 inch and the 12 inch together a i have 4 speaker wire runing from the Amp to the subs two for each.