Relay rating for headunit?

Hi guys, I wonder if someone could point me in the right direction here? I have an Alpine Sat Nav system, and it is a real pain that every time I stop for fuel etc and start the car again that I have to wait for the whole system to boot-up again, so I was thinking of wiring the ACC 12v+ to the permanent battery live via a relay and a timer. The idea being that if I need to remove the keys from the car I can hit the switch which will throw a relay over for say a maximum of 10 minutes, and timeout thereafter if I do not return. My questions are:

1. I have seen a timer/relay module that will do the job, but it is only rated at 5A, I was wondering if this will melt trying to run a Navi Unit, headunit and CD changer?

2. Even if this worked, would the current drain caused by starting the car again reset my navi unit anyway? If so, is there any possible solution? a big cap maybe?

Thanks in advance for any advice, scribla.