My car was stored in the garage every year from November to March and I started it every month and left her to run for 1/2 hour or so. This spring I changed the original Varta battery that had been in it since November '03. The battery had never once failed but I thought 5 1/2 years was good enough and why take chances. No tender or charger etc was ever used, so I am not going to start now. If the car was left unattended with a tender on it I would not feel easy as you never know what could happen.