How do I match motor and battery leads on a generic e-bike conversion kit?
Based on the info you've presented, its "cross your fingers and hope"

Can you tell us anything further about the motor, motor kit?  Even a manufacturer could help.

My ebike kit used 7 pin DIN connectors with a screw-on barrel lock ring.  The battery connectors were generic automotive spade connectors.  

If you're choosing a connector, then voltage and current (ie wattage) is relevant, as is whether you want to hot-connect them.  Plus you need something that is water resistant and vibration tolerant.  (note spade connectors are neither of these... guess how I know that!)

Final thought - you're talking about a kit.  In my mind a kit comes with everything you need to do the job, possibly excluding batteries themselves.  However any parts not included will be common and well-described.  

And what's wrong with a splice?  A properly-done connection will outlive the wire.