The Trojan battery web site has some good info in their FAQ section. Click on this web link:
http://www.trojanbattery.com/tools/faqs.aspx
A good way to check battery condition is with a hydrometer. Specific gravity readings are contained in Trojan's application guide at this web site:
http://www.trojanbattery.com/pdf/UsersGuide_English.pdf
Hydrometers can be purchased for less than $10 online.