I'm stumped

750ah battery tender I got at harbor freight. I didn't need the other cables it came with so I cut, strip and solder. Made a little extension cord, it has double in line fuses but both are at same amps.

Didn't work. This is a SAE connection, meaning it completes the circuit when they are connected.

Didn't think of that, found a SAE to SAE 12ft extension cord on Amazon, it has reverse polarity adapter for the circuit doesn't complete when joined.

Still doesn't work. Is it the charger rejecting the additional resistance? Anyone ever made an extension for a tender?