Friend gave me booster pack with dead battery. I see it has a 12v 18aH sla battery. Battery is 7x7x3". Some info online says it is AGM and lead acid with mini plate design. Does gell mat design use metal/lead plates? Thought they were rolled up tubes? Or is that optima tech? So how can a 18ah battery provide 1000 amps of instant power? A generic like sized battery is $40 online.