Warren Buffett shelled out $2.1 billion on Bank of America stock over 12 consecutive trading days, boosting his stake in the banking giant to almost 12% as of August 4.

Berkshire is Bank of America's biggest shareholder, and Bank of America is the second-largest holding in the company's stock portfolio after Apple.

Bank of America's interest income is also under threat from the Federal Reserve's unprecedented efforts to shore up the US economy, Stephen Weiss, managing partner of Short Hills Capital Partners, said on the program.

"There's a new valuation normal for bank stocks and I think you're at it right now," Weiss added.

Sarat Sethi, managing partner at Douglas C Lane & Associates and a Bank of America shareholder, was more positive about Buffett's latest bet

"We think that bank stocks have the potential to increase by 50% over the next 18 to 24 months," he said, adding that Buffett is "on the right track" with his Bank of America purchases

Here's a chart showing Buffett's purchases of Bank of America stock and the bank's stock price in recent days: