Can't you just pedal it?
Is that electric? If so, try the electric bike forum.
Bikes: Old steel race bikes, old Cannondale race bikes, less old Cannondale race bike, crappy old mtn bike
From the second picture at least is noticeable that the cables are not connected to the batteries???
How you can buy something w/o instructions?
You need three Maintenance Free Lead Acid Batteries number 6-DFM-12A 12V 12Ah. If you put in that number you should find the batteries in the states for about $32 each. When you get them just slip the clips to the little posts on the batteries and hope everything else is OK. Turn on the key and turn the hand grip. Away you go. I hope you have the cover for that battery box it screws on with 5 screws and you need the charger to plug into the round port in the end of the heavy box with the 3 batteries inside.