As asked previously, the age of your batteries are pretty important. If you are not the first owner of your MH and don't know when your batteries were installed, you can look on the top of the batteries to see if there is an installation date punched out on the tag. If you have owned your MH more that 4 years or so and have not replaced the batteries, I'd bet it's time to replace them.
Here's a link to a web site with information on deep cycle batteries, including how to test them. There is also information on how to maintain your batteries. Be careful about having your batteries tested at an auto parts store. Deep cycle batteries should be tested differently than regular car batteries.
Pacific Power Batteries - About Automotive Batteries