By 10 p.m. Sunday, the outage map on Peco's website showed 22,855 customers without power across the region, down from nearly 71,000 at 6 a.m. - and 623,000 at the peak, Maher said.
Overall, Peco's figures show, about 715,000 of its 1.6 million customers were without power at some point during the storm.
In hardest-hit Chester County, about 10 percent of households, nearly 21,000 customers, remained without electricity - their fifth straight day in dark, frigid houses. Temperatures dropped into the low 20s by Sunday evening.
More than 6,000 utility workers and back-office personnel were repairing systems in what is the biggest winter outage in Peco's history and the worst since Hurricane Sandy.
Towns with the highest percentage of customers without power were Charlestown, East Nantmeal, Newlin, and West Vincent in Chester County.
A Montgomery County municipality - Lower Merion - had the largest number of customers without power as of 1 p.m. Sunday: 2,596.
Township Commissioner Jenny Brown expressed frustration.
"I completely understand and agree that progress has been too slow, that Peco's response has been insufficient, and that Peco's communications have been unreliable and unsatisfactory," Brown said in an e-mail to township residents.
Inaccurate communication was the main gripe of Buckingham resident Jeff Gale, whose family was in its fifth day of huddling around a propane fireplace to keep warm.
Gale, 46, said that for several days, Peco said power would return to his neighborhood by 11 p.m. each night.
But on Sunday evening, he said, the time was yet again pushed back - to 11 p.m. Monday.
"The most frustrating part is just that you cannot get accurate information," he said.
Steve Freemer of Huntingdon Valley was also outraged by constantly changing estimates of when power would return.
He said his wife, who has cancer, stayed in their home Wednesday and Thursday night because Peco suggested power would return each night.
On Friday morning, Freemer said, he drove her to her sister's small apartment in Jenkintown, where she'll stay until the heat comes back.
"I would have taken my wife out of here sooner" if the estimates were accurate, he said, adding, "I don't want any special privileges, I just want to be told the truth."
Farther west on the Main Line, Jennifer Schu of Strafford had seen crews working near her home.
"I'm grateful but I'm confused as to how it can be this long," said Schu, who has lived there more than 13 years. Strafford was still without power as snow began falling Sunday evening.
Critical facilities, including hospitals, emergency-response centers, and schools are the first priority, Maher said. After that, crews have to restore power based on the number of customers served by a circuit, he said. That usually means fixing distribution lines closest to power substations.
"It really depends on where you live," he said. "Are there trees? Is it rural?"
Wooded areas provide more challenges. According to Maher, wires and poles can be damaged in multiple places along the same line, slowing the process.
"There's no typical jobs in these settings," he said.
The last step is to reach the people on single distribution lines, which tend to be rural homes farther from transmission lines and substations.
That means as more power lines are restored, the numbers of people brought back on line at any given time are less dramatic.
According to Maher, no preference is given to commercial or residential customers. Peco did not give an estimate for when power was expected to be fully restored to the region.
A shelter at West Chester University had 26 guests Sunday evening, down from 45 in the morning. The most-used services were warming, food, and water, Patty Mains, spokeswoman for Chester County Emergency Services, said. The shelter will remain open until 7 p.m. Monday.
Peco scheduled public forums for customers in Chester, Bucks, and Montgomery Counties for Sunday and Monday.
Meanwhile, workers have come from as far away as Arkansas and Canada, and crews from New Jersey's PSE&G have joined the effort. The utility sent more than 100 workers, expected to put in 16-hour shifts for the next three to five days, the company said in a news release.