$35 with free shipping is a good deal
you dont have to spend a lot of money on the battery for a 650. The bike hardly loads the battery up at all, it has no key fob or other electronic junk that is constantly draining the battery down when the bike is not running, so that first battery listed by Les will last you 3 or 4 years.
The thing you have to get right is make sure the battery from a website is listed for your motorcycle make year and model, otherwise it wont fit into the space on the right side under the seat, and the red + and black - battery terminals may be on the wrong side, and the wires wont reach.
Installing it is pretty easy with a screwdriver. Pull the black (-) terminal off the old battery first, and put it back on the new battery last.