Battery Tender Jr. Used it on three bikes and one car over the last six years.

 

I have had a Battery Tender Plus for 5 years and it is great. I connect a pigtail for my bike so I can easily charge it during the winter months. I also bought the alligator clips to charge my riding lawn mower battery. I used the third connector option available to charge my two BMW bikes several years ago through the special 12v outlets they have. You can leave the charger connected without fear of overcharging the battery. IMHO it's the best one out there.