Sealed V.S. Ported power use

[youngvermonter]

I have two Rockford Fosgate P3 Punch 12 inch speakers paralleled into a Hifonics 1200 watt Zeus amplifier at 1 ohm. I had my speakers in a ported box, and had no issues with the amplifier overheating or battery usage. But in order for me to fit my tools in my trunk I downsized from the ported box to two sealed enclosures, and the alternator cannot keep up now, and the amplifier gets hot and shuts down. I didn't change the power or ground setup at all when I changed enclosures, so the only think i can think of that would cause a difference is the box requires the  subs to draw more power. I am quite frankly at a loss, and if changing back to a ported enclosure will help I am more than willing to.