Signal Dynamics made what use to be the cleanest, basic volt meter, which had a 3 color LED voltage status indicator. Problem was it was NOT rated as waterproof, had significantly higher wattage consumption (compared to Signal Bright shown below), had a bulky remote circuit box which required separate mounting, and was very bright at night. Worst part was, many reported short life-spans. Mine failed after only 6 months.
Next "Batter-Up";
Spark Bright.This one has miniaturized circuitry, auto-dimming for better night time display, and is waterproof and shockproof with pending IP rating.
You tell them what type battery you are using (Lead/acid, Lithium iron Shorai, etc) and they will program it to be compatible at no extra charge.
In my case they reduced the over-current warning from 15.2V to 15.0 volts to Shorai spec's.
They are available in two main variants, dimming or non-dimming, each variant is available in several sizes with either convex or concave bezel.
They have a very easy to understand and memorize chart for interpreting the 3 color LED status light, which is reportedly easy to read in direct sunlight.
Also they have VERY detailed and easy to understand PDF's that guide the user through proper use, function, and product details.
I ordered the Shorai Spec 8mm Eclipse version (auto-dimming) with convex bezel.
Will report how install goes with pictures.
Available here;
http://www.sparkbright.co.uk/sparkright-eclipse-battery-voltage-monitor.php