Look into getting some old pallet jack batteries or fork lift units .... most are OK but will not work for full 8_hour shift (diminished capacity) .... those things are the way to go. Otherwise if you have big bucks ... use excide 2-volt cell banks on racks. Commercial systems use that approaoch. My suggestion is to go find a waterfall or falling stream and tap into it.
If you are going to use auto batteries ... look into Optima spiral wound cells ... $150 - $200 range for massive capacity ... but match to daily usage requirements.