This little USB charger is a must have in your camper to keep your phone charged at night. The displayed voltage is a great way to see if you solar panels are charging and estimating how empty of full your battery is. A convenient On/Off button allows you to stop electronics from continuously using the battery without disconnecting them (wireless phone chargers, radios etc...)
 
A common use of this product is to have one as a replacement of the original 12v outlet connected to the starting battery and one at the back connected to the deep-cycle battery. This allow for a continuous monitoring of the state of charge of both your batteries. The blue light is more suited for visibility in strong lighting (front area of the vehicle during the day) and the red light version in darker areas not to disturb night vision (sleeping area). You can also close the rubber lid at all times to block the light. 
 
Comes with a 2 year warranty.
Includes crimp-ready connectors
Stand-by voltage usage when on is around 100 mA (1 Ah every 10 hour)
Stand-by voltage usage when off is 0 mA