As Hurricane Sandy made its way to the Washington area last month, residents didn’t just load up on bottled water and batteries. Many also looked to withdraw extra cash to prepare for possible power outages that would make ATM withdrawals and credit card transactions impossible — serving as a new test of the banking system’s continuity plans.

Sandy Spring Bank began filling its 44 ATMs with cash the Friday before the storm, and again on Saturday and Monday.

“We make sure that we stock the ATM to the max if there’s a possibility there’s going to be a storm or power loss,” said Ani Simonian, retail administrator for the Olney-based bank. “When there’s a blizzard or a hurricane, people tend to hit the ATM more often and withdraw more cash than they normally would.”

Banks and credit unions, which are required by regulatory agencies to have expansive disaster relief plans and secure backup networks, say the immediate challenge during unexpected emergencies and power outages is making sure customers have access to the bank’s services — and cash.

M&T Bank made arrangements to have vendors service its ATMs before the storms hit. Of its network of about 2,000 ATMs, 200 lost power and one machine in New York’s Hudson Valley ran out of cash.

“It’s not so much a battle of an internal or systemwide computer failure,” said Mike Zabel, a spokesman for the Buffalo-based bank. “It’s about localized access — dealing with infrastructure like ATMs and telephone lines and power lines.”

It wasn’t just ATMs and banks that were feeling the pinch. The Harris Teeter in Adams Morgan, which generally allows customers to take out up to $200 using their debit cards, limited cash-back transactions to $50.

Many financial institutions in the area said they were prepared for the storm, thanks to monthly on-site emergency simulations and drills.

“We have a whole disaster recovery plan for all locations,” said Susan Riel, senior vice president and chief operating officer of Eagle Bank. “Our whole network has generators and backup generators.”

Navy Federal Credit Union had to shut down 40 branches that lost power on Monday and Tuesday. Late last week, two of those branches remained closed.

“Overall, our infrastructure is designed to be resilient,” said Jeanette Mack, a spokeswoman for Navy Federal Credit Union. “When storms did hit, we were still very much operational — we had online banking, mobile banking, people could call.”

At Sandy Spring Bank, the staff prepares for large storms by bringing in trailers with backup generators and arranging for extra diesel fuel to keep backup systems running.

Earlier this year, after the derecho thunderstorms swept through the region, nearly 20 of the banks branches lost power for up to four days.

The branches stayed open anyway. Employees processed transactions manually, and the bank brought in fans, ice and water to keep customers comfortable.

“One branch had popsicles they were passing out,” said John Sadowki, the bank’s chief information officer. “Being a community bank, you really just have to be there for your clients.”