Optima battery question

[19sixtynine]

I bought a used yellow top, put it on a "battery Tender" brand charger and left it for 3 years while I worked on my car. I thought for sure it would be a goner, but nope, it fired the car right up and continues to run strong. I've been driving the car since November and when I pull it in the garage I jsut hook it right back up to the tender. I own 2 battery tenders and love them, never had a problem and have been using that brand for about 10 years on various cars, bikes and boats.