I think the Battery Tender Jr's fuse is in the pigtail, not the charger.
If your existing pigtail does not have a fuse, swap it for a fused one. I've used multiple BT Jrs for many years on multiple bikes and other things, and have never blown a fuse, but they are still a good idea. Fire is always a possibility with these things.
You can buy extra pigtails and extensions for BT Jrs without buying a whole new unit.
http://www.batterytender.com/ (but Amazon is the place to buy for best prices)