B737 Captain reported an incomplete lithium ion battery document was provided to the Captain during pre-flight. The Captain; with the help of the First Officer was able to obtain the missing information prior to departure.

Narrative

Shortly before departure a pink battery powered wheelchair or mobility device for was passed up into the cockpit. The only box checked was the one next to lithium ion battery. Neither X or Y below that was checked to indicate the status of the battery. The person accepting the form did sign it but that was the only other information filled out. The FO yelled out his window at a ramp agent who came up to talk to us about the form. He said he knew nothing about it as the person fills that out and gives it to us. He then went to find the person. They both went down on the ramp and soon I saw another ramp agent or two join in the discussion down below. Eventually they checked on the wheelchair and filled in the appropriate boxes indicating that the battery was attached; power disabled; and key tuned off. The form was brought back to the cockpit and I quickly pointed out that the form says to 'applicable sections' and 'cross out non-applicable battery types'; neither of which had been done the first time. We departed X minutes late and the flight feed delay was charged to customer with wheelchair. This would have been an on time departure if the form had been filled out properly in the first place.