Be sure the battery is fully charged and the terminals are not corroded. Clean them thoroughly and apply dielectric grease when re-attaching. If the battery wasn't properly cared for, particularly over the winter, it could be weak after three years.
I almost replaced my genset start battery this year. It would turn the motor over for a second or two and die, without starting. I would wait a few seconds and hit the start again, after the battery recovered a bit and she jumped to life. This was because she was primed up, after the first attempt. When I went to remove it, I found the terminals were corroded. After cleaning, as described above, and replacing one of the connectors, she works like brand new.