The Echo Charger is about 6" x 6" x 1" thick and has 3 wires coming out of it. Here's a link to a web page with a photo:
On that same page, you can click on Document Downloads and go to another page with links to an Owners Manual and a Data Sheet.
I also own a 2004 Alpine and I've been told that 2004 may have been a transition year from coaches having an Echo Charger to coaches not having an Echo Charger. So, you may not find one. I haven't looked too hard yet but I have not seen one on my coach either.
Regarding the batteries, I went down to my local Interstate battery dealer (a local rental supply outfit) and ordered up the batteries. BUT I forgot how important it is to get the right battery terminals spec'ed out in advance. I didn't specify the terminals and didn't get the terminals I wanted. (The coach had batteries with a horizontal bolt holding the cable to the terminal and I received batteries with a vertical bolt; I just barely made one connection work with the length of the cable.) So, you should maybe take a picture of the existing (factory) terminals and go to the battery dealer and tell them you "must" have those terminals.
Battery water fill: The previous owner of this coach told me that he just pushed the battery water-fill button and held it until he saw water returning thru the tube to the reservoir and that was his indication that the batteries were full. I tried this and the batteries were not getting filled. The procedure I now use is to mentally note the water level in the reservoir (or hold my fingernail there), then push and hold the button to energize the pump, then water the reservoir level until it quits falling. Then the batteries have taken all the water they need.
There are many brand choices and it seems that people have their favorites for various reasons. I've had good luck with Interstate batteries and they are easy for me to get hold of. You may find other brands easier to come by. But, you want to be smarter than the salesman. Take a look at this page on the Interstate website: http://www.interstatebatteries.com/c...olf_f.asp?js=1
You'll see that you can get 6 volt Deep Cycle batteries that are all the same physical size but in many different amp hour capacities and weights.
The 2004 WRV Brochure states:
2 Interstate« 660 CCA @ 0┬║F maintenance free
starting [chassis] batteries
(6) 6-volt batteries
w/732 total amp. hours (house)
So, that tells you that WRV installed the U2200 battery as the house battery (see the chart on the Interstate battery webpage). You might want to take this opportunity to buy the larger capacity U2300 or the U2400 battery and get more capacity. I think if I did a lot of boondocking, I'd opt for the higher capacity depending on the price.