I have 14 years on mine ---I never use a battery tender, I let it sit in the car hooked up all winter, I expect it to start, If it won't start I expect it to drive the car out of the garage (if I start driving it out on the starter it usually starts 1/2 out of the garage)
The only time it was dead was when I left the key on ---I have a small charger, hooked that up, hand cranked it (was late, needed to go)
I use a stock generator, diode cutout, no voltage regulator --I use the Halogen headlights to control the charge( drive with lights on)
All the people that I know that use batt tenders replace their batterys much more often than I do, my batterys thrive on neglect, when I was using regular 6V batterys I would get 7-9 years out of them.