Similar sounding problem with my 75D a few years ago. Replacing the starter cured the problem. Two issues though - the starter was a real pain to replace (one mounting bolt is very difficult to access) and I did get a "bad" starter which was replaced under warrantee after about 6 months.
There is no separate battery for the generator. Starts using house batteries.
Should add that I bought the first replacement starter online but then found a local starter/generator repair shop that supplied the same starter at a lower price with no shipping.