Take it back to best buy. Don't know this amp installed but heavy amperage of a lot of aftermarket amps are wired direct to battery through fuse. This doesn't cause massive amp draw in standby but it does keep large capacitors charged which does draw some current. They can put you a manual switch inside or install a relay circuit operated by ignition switch.

 

I really like your setup. But does one have to live with that surround piece that protrudes from the dash? ... can't say I love that. I'm debating whether such a thing is worth it though, because the larger iPhones have pretty big screens and it's exactly the same info.