I run an antigravity 16v race battery, weighs alittle over 4lbs. Did a test to see how many times it would start the car and run it without charging, but I ran out of fuel before I could find out. Started the car and ran it for 3 1/2mins 10x's before I ran out of fuel.. Electric fuel pump, msd, etc. After the 10 times the voltmeter showed 16.7v and it took 25mins to bring it back to full charge. You can get them for around a hundred less than what their online store shows if you have a local dealer. Pretty awesome battery to hide in a factory case...