Customer satisfaction ratings of the major banks have maintained their steady long-term upward trend, despite recent fluctuations.The latest Roy Morgan Research survey of small business owners, conducted in March, puts the average satisfaction score for the big four banks at 64.4 per cent. Over the past five years that rating has climbed steadily from around 55 per cent. The big banks have put a lot of resources into improving customer satisfaction and the investment appears to have paid off.Even National Australia Bank, which has suffered a sharp fall in customer satisfaction since late 2007, has a higher score than earlier this decade.Westpac has the highest satisfaction rating among small business, with 67.5 per cent of its customers saying they are satisfied with the bank.ANZ has a rating of 67.1 per cent, Commonwealth 65.4 per cent and NAB 56.3 per cent.