I worked at a Batteries Plus store for a couple years, and was always looking for information that would help me help our customers. One site that I found quite useful is batteryuniversity.com
While much of the information is more than any of us will ever need, there is still a huge amount of useful stuff that RV owners can use. Besides covering all aspects of lead acid batteries, you can also learn a lot about lithium polymer batteries, used in our cell phones, and other household batteries. Give a look and see what you think.