It's likely that's the original converter sold with the rig. As I recall they produce a constant 13.6 volts and are often referred to as "batter eaters" because they ten to boil off the battery water. Many people spend $150 and upgrade to something like http://www.amazon.com/Progressive-Dynamics-PD9245CV-Converter-Charge/dp/B000GANZZ6. Easy install with lots of "how to" on the web.
At any rate - you can test your existing converter by either measuring the voltage at the converter (best way) or measure it at the battery when the rig is connected to shore power ... should read around 13.6.
