You need to find the pilot cell. It will be near the positive or negative terminal. One of the bus ties (long lead connectors between cells) will have data stamped onto it. Depending on the brand it will be easy to read or in some strange code only the manufacturer knows. A good battery manufacturer should make the information available on its website. Do the voltage checks mentioned above and determine the battery's age.
Warning! I don't know very many people who take the battery seriously or have the experience or knowledge (even at battery places). If you find someone who knows about batteries, keep in touch with this person. Get a second opinion on all battery repairs or service.
The Crown brand tolerates battery problems very well so you shouldn't have to do much more research or testing.
Understand that most batteries have a life of about 3 years, I don"t care about the design,etc. Nobody takes proper care of their batteries, very few know how.
Try to have a new battery within a year and get the battery manual for the brand you have (should be able to download off the website).