I solved a number of problems with this upgrade:
A. Everyone gets on the boat with a dead cell phone battery and wants to use my phone to take pictures of their kids/spouse/etc. Then I have to send them the pictures.
B. I have the only 12V plug at the helm and others want to charge their phones.
C. My kids want to listen to their devices but I don't want to set up the bluetooth to connect to their devices.
D. I have a nice volt meter for the engine battery on my dash but don't really know what voltage my house battery has unless I pull out the volt meter in my tool box.
So I installed 2 items in my glove box.
1. USB Volt Meter (tied into constant 12V from my house battery so we could charge phones even when the engine is off)
2. AUX (3.5mm jack) input and connected it to my Clarion M606
Added to my AUX1
Put it all together with a few careful holes in my glove box (at 11.3 volts it looks like it's time to charge the house battery):
Now all 4 problems are solved. I keep a few different USB charging cables for different types of phones and we are off to the races. The phones/devices can charge safely in the glove box and spool tunes straight to the Clarion M606 head unit.