A recent study found that more than 1 in 3 people with checking accounts at a large national bank feels scammed by ever-increasing bank fees.

The 2015 Consumer Banking Insights Study found that even though 92 percent of bank customers say they are aware of fee structures at their banks, 36 percent of megabank customers still feel scammed.

Millennials are the most likely group to feel this way, according to the report, which found megabank customers are twice as likely to feel scammed as those who use a community bank or credit union. Thirty percent of millennials feel this way compared to just 16 percent of adults over the age of 55.

The most hated fee? Thirty-one percent said it's those monthly charges banks impose simply for entrusting them with your life savings. In the last six months of 2014, the average monthly checking account maintenance fee was $12.87, up 18 cents from the previous six months, according to MoneyRates.com. In order to avoid this fee, customers on average must keep about $5,700 in their account at all times, $268 more than the required minimum for the first half of 2014.

When considering only large banks, customers must maintain an average balance of $9,780 to qualify for a waiver of those monthly fees. The average checking account costs $154.44 per year simply to maintain, according to MoneyRates.

The second most hated fee, at 26 percent, was ATM fees, according to the study conducted by Harris Poll, which surveyed 1,002 adults online in January.

The study found that 2 out of 3 respondents would prefer to use a community bank or credit union than a megabank, if everything were equal.

A separate poll released in January found that 58 percent of likely voters would support breaking up "big banks like Citigroup," reported The Wall Street Journal.