Electric Bike Wiring?
Your 48 volt motor probably uses some modern flavour of lithium battery.  It will probably refuse to run on anything less than 44-46 volts (actual numbers may differ) and this will be in the controller's manual.

If you're using 12 volt SLA lead acid batteries, then they must not be discharged below 10.5 volts per battery, which would be 42 volts in your scenario.

To get 48 volts, you will need 4x 12V batteries in series not parallel.  12V batteries in parallel will still only give 12 volts, just a lot more current for a lot longer.  Since your motor is 48 volts it won't even start on one 12V battery.

I recommend you use the fattest wires you can to link your batteries.  Electric cars eschew wires in favour of busbars for added cross sectional area.

If this sounds like alien gibberish, you should enlist the aid of an electrically-minded assistant.



As an aside, you'll need to change a lot of how you ride once you have that much power on tap.  Riding in the door zone becomes a game of Russian Roulette, and you'll have to ride much more defensively, which means scanning ahead, eyeballing possible threats, and anticipating what might happen.  

Also some locations would call a 1000 watt motor an electric motorbike, not an assisted pedal bicycle.  You may need to check this out.