A limitation of maximum amps of the battery less than full throttle motor demand amps mainly means you need to stay off of the throttle. Full amps would be drawn by full throttle, but the controller would use less if you didn't demand it. then you could stay in the limitation of the battery current limit. So don't try to go really fast. Or climb steep hills.
Totally dead should be another problem, like you don't understand the hookup or the plug/receptacle is wrong or something.
If your meter has sharp enough points on the probes (rare these days) you can pierce the wire insulation after the connection to the battery, to verify that you are getting 36-42 V to the controller input wires. If so, reinsulate the holes with duco cement or windshield weatherstrip adhesive. If not, repair the connection.