If battery is not close to full charge, it may take a whole 24 hrs to reach full charge and turn green. They only charge at 750ma -1.5 volt so they can take a while. Mine is a deltran battery tender junior 750ma and it will take 1/2 to 1 hour to turn green after I get home from riding and plug it back in. I keep mine plugged in year round, my battery in my heritage lasted 8 years.