As batteries age, and the temperature drops it will take longer to reach a full charge. The charging systems on my bikes are all in good order, but as time goes by, it can sometimes take overnight for the light to go a steady green. Worry when you don't see green, or the flashing green never stops. When the flashing green doesn't go to steady green, that battery has reached an age where the charge it can take, is not as high as the battery charges thinks it should take. This is when you can take a serviceable battery, and fry it from an overcharge. I can understand your being a little apprehensive from the last event with your bike, but stop looking for problems that you don't have. BTW, one you get a solid green light on the tender, disconnect it. Leaving it connected may cause more harm than good.