Air carrier Captain reported receiving incomplete and erroneous DG documents and refused to push. After talking to the DG load planners; it was determined that Airport Operations did not properly complete the load planning paperwork as it did not include a battery-powered wheelchair that had been loaded onto the aircraft.

Narrative

Report showed passenger had WCBW (Wheelchair with Wet Cell Battery). Gate Agent did not provide form. After multiple requests and my refusal to push; the Gate Agent eventually provided an incomplete form that did not show the battery location. After asking; she admitted that the battery was in the passenger's carry-on luggage; which violates FOM. After showing the Gate Agent our FOM references; she stated that this is the way we always do things in ZZZ; and that the passenger is a frequent flier who always keeps her battery. I called the Dangerous Goods (DG) load planners for assistance; and they stated that there were no wheelchairs loaded on the flight; in spite of WCBW being listed on the reconciliation report; and the fact that I saw it being loaded. Load Planning concluded that ZZZ Operations did not properly complete their load planning paperwork. It appears that ZZZ found a loophole that enables them to save boarding time and bypass standard DG notification procedures. Had I not looked at the FOM and WCBW requirements; I would have transported unauthorized dangerous goods in the cabin.