After the financial crisis 10 years ago, unhappy customers were expected to flee the megabanks for smaller competitors. It didn't happen. And the big banks became even more entrenched. Now another wave of alternative banks are at it again. Chime, the biggest new name to pop up, has opened two million fee-free online checking accounts and is adding more customers each month than Wells Fargo or Citibank. Venture capitalists are pouring money into American start-ups that are offering basic banking services - known as neo-banks or challenger banks. In 2018 so far, American neo-banks have gotten ... 10 times as much funding as they did in 2015. "In consumer banking, you have what is one of the largest industries in the United States, in terms of profits, and at the same time one of the least disrupted industries, and the most unpopular with consumers," said Andrei Cherny, the founder of Aspiration, a neo-bank that has attracted nearly a million customers. "Those three things create a perfect storm for disruption." The banks are struggling to adapt because they have built an expensive infrastructure of local branches and have become increasingly reliant on revenue from fees. Surveys have shown that a wide array of fees, for everything from A.T.M. use to checking account maintenance, have been steadily rising in recent years. The big banks have also held on to the interest payments they get rather than passing them along to depositors.