Bottom line, for $1,500 you can get all the scuba you need. you can get a bunch of tanks so you don't have to drive to the shop every day. and they will be easier to transport to the dive site. Car batteries are heavy and if you have a enough of them to run a compressor adequately, you will have to start thinking about little problems like getting enough draw on your house hold current to charge them in a timely manner. When your wife sees what happened to the electric bill she will also have something to say. And don't forget about the shock/ fire hazard created by trying to set up a bank of batteries for a day of diving. If you are planning on using it in a river, you will do better with a SCUBA rig. Surface supplied air in a current that might have things like trees and other debris is just an entanglement waiting to happen. a slack hose getting caught under a branch will prevent you from getting to the surface. then you have to evaluate how to untangle it and get topside safely in a bad situation... possibly without your reg. all this sound like you just want to save yourself driving to get air fills. Not worth it.