Blue Sea 1733 OLED DC Power Meter

Blue Sea Systems is a world leader in high-quality onboard electronic components.  

• displays DC voltage from 8-36VDC. 
• OLED display is easy to read in practically all lighting conditions.
• Resolution of 0.01vdc
• Mounts in 1-1/8" (28.58mm) hole
• Simple 2-wire hookup
• Rear has 1/4" tabs for you to connect your mating connectors/wires to
• Threaded neck with nut allows easy and secure mounting through surfaces up to 1.25" thick
• Reverse polarity protected
• Lifetime warranty
• Waterproof
• Available in Yellow or Blue OLED display

Manufacturer's web page is here.  Instruction manual is here.