*The NAV system will come on with the acc setting.

*On the Nav system there is a way to shut down the display, I think it is "Menu" then "Display settings" then "Turn off display", this will leave the system running with no display.

*Also I think that using the 110v system will draw more power to run a radio then just using the 12v jack next it. the 110v outlet is using a power inverter to convert the voltage from 12v DC to 110v AC then your portable radio will convert the 110v AC back to 12v DC. This will waste a lot of power in conversion. Best bet is to power a portable radio directly from the 12v jack, and you won't need to have the key set to acc because that jack has power with the ignition off. This will save even more power because you won't be powering all the extra stuff like the NAV system at all.

* another thing you could do is get a marine "Deep cycle" battery and just power the radio from that battey, then you won't have to worry about the car battery at all.

(note: a deep cycle battery is made to allow you to run it almost out of power and it will still take a charge. A normal car battery can develop problems if they are repeatadly discharged past 75%)