up to my already charged battery and the light never changed from red to green. It always showed red, so I think that means it was continually trying to charge it. I removed the battery tender to check the voltage, and it was over 13 volts (engine not running). I had it connected for about 24 hours.
I tried it once more after that and the same thing was happening, and I haven't tried it since. Do you think I have a faulty bettery tender unit?