Making up battery cradle power connectors

So I converted another one of my old bikes to an e-bike and I want to share the battery with the first one. It's a 52V EM3EV Super Shark type. I bought another cradle to attach to the new e-bike but unfortunately it didn't come with a power wire pigtail. I have been trying to solder some wires on but nothing sticks to these terminals. What do you guys do for this type of connection? Pic below shows the EM3EV cradle wires and the terminal block from the new cradle.

I got this resolved. Used a Dremel to rough up the contacts and the solder stuck.