What make is your battery tender? If it's Deltran, they stand by there products.

 

The fuse in the pigtail checks good, the charger is a Moto/Stance and is sealed. I may cut it open just to see what I can see. Actually I purchased it on-line over a year ago because it was on sale, 19.99 I think and just got around to installing it. Sometimes you get what you deserve. Ouch!

 

I have used the wal mart brand ones. Been using them for years and on my bike, four wheeler,seadoos and lawn mower. They work great for me. Plus only $25