A 15 Amp (that's 15,000mA) charger for $30? That's a Rollecks watch. (IOW, a piece of junk.) The standard Samsung 2,000mA charger is a little less than half that price. There are 15,000mA batteries, but I haven't seen any charger with a 15,000mA output. (The battery doesn't put out 15 Amps, it stores 15 Amp hours, which you can draw, in a phone, at about 500mA per hour [which is about what a phone uses], which means 30 hoursa of use if you don't want the battery to last very long (you don't discharge lithium batteries to less than 40% if you want them to last.). A charger that puts out 15,000mA couldn't deliver it through a microUSB connector - the microUSB connector is rated at about 2,000mA maximum. So delivering more than 2,000mA (2 Amps) requires something other than a microUSB charging port.
As far as external batteries, the concensus seems to be that Anker is among the best. ZeroLemon is also supposed to be good.
@dragonsamus:
They're batteries, not chargers. They have to be charged. Chargers don't have to be charged, they do the charging.