The LED you are looking for is (hopefully) green. If it's red, there is a problem. The code is written on the outside of the casing.
The unit was actually pretty hard to find. It was really tucked up into the framework and well hidden. I found mine exactly in the middle, between the rails, hanging from the ceiling above the inverter. The picture Mike mentioned is the same as mine.
You might also do some research on the new batteries. There are numerous threads on the pros and cons of each. I've found that the extra cost and performance of the AGMs easily paid for the price increase over the flooded cells (based on only 9 years and two coaches). The extra capacity and assurance are pure gravy. For AGMs try Lifeline (Azusa area) or Sears, for flooded cell try Interstate or Sears. I only mention Sears because they have a good price and unbeatable warranty. With our fleet of trucks, it has worked out VERY well, and they are fast. Their AGMs for my chassis work well. I have Lifelines for the house.
2003 Alpine 40FDTS (400HP)
Long Beach, CA