Have you checked your fuses? this is the most likely easy fix for this problem.. Unhooking the battery should not have done anything to the radio. You either have a fuse issue, or a bad radio.
The P1684 code simply means that the battery has been disconnected within the last 50 starts.
It is behind the battery.
It's in park or netural. It has no fluid in it. the engine is off. the linkage is disconnected.
It is under the hood on the driver side.
Under the hood by the battery.
It is next to the battery.It is next to the battery.
The yellow dipstick near the battery.
Under the hood next to the battery.
No
It could be your starter, or your starter solenoid.
The 2002 Dodge Grand-Caravan has 12 valves.
The 2014 Dodge Grand-Caravan has a V6 engine.