SAN FRANCISCO — That banks routinely process their customers’ debit card purchases to maximize overdraft fees is an allegation that’s sure to make a juror’s blood boil.

But it will be up to U.S. District Judge William Alsup to decide a California class action accusing Wells Fargo of the practice. The bank squares off in a bench trial Monday against lawyers from Lieff Cabraser Heimann & Bernstein, and plaintiff damages estimates top $300 million.