I don't believe that your problem is related to the batteries. As an additional check you could also get a hydrometer to verify that the specific gravity is correct. I am guessing that it is and, if so, there is no reason to replace the batteries based upon this one specific problem. However, if these are your house batteries (deep cycle style) you will also need to ensure that it will power everything else you use in the coach for the period of time you are not connected to shore power. For many folks, that's only the time between leaving 1 park and arriving at another or arriving at home so very little capacity is necessary.
As to the slide issue, if you are outside and the wife pulls the slide in, can you push the slide ever so slightly at the beginning of the cycle and eliminate that strain? Also, as mentioned above, have you lubricated all visible areas where you have metal on metal or metal on plastic glide? If there is plastic, is it still nice and smooth or chewed up enough that it needs replacement.
Others obviously disagree but I don't believe you need new batteries and should be looking for a different solution.