Where can you buy batteries online for cheap?

I am looking to purchase a 7.4v 5amps battery or 12v 5amps battery

if you know a trust-worthy site with a deal around $12 or less please let me know

i have a corresponding question as well, if you power something with two batteries of 6v 5amps, are you using 12v 10 amps?
p.s. U.S. only please

If you want 12V @ 10A you'll need 4 batteries. Break them down to sets of 2 batteries and wire them in series. Then take those 2 series wired sets and wire them together in parallel. If you don't know what series and parallel wiring is then look it up.
depends on how you wire the batteries together. If you connect the batteries parallel to each other then you double the amps, if you connect the batteries in a series you double the volts but the amps stay the same.