"The first bad news to greet him [Otis] when he walked in [from work on the farm] was that the car battery was dead. / "We can get it recharged," he said shortly, heading for the dinner table. / Elsie, his wife of seventeen years, shook her head. "Mart Petersen says it's shot," she replied. "Lord, it's been in there since we got the car six years ago, so it's high time it went." "
It would appear that Petersen worked as an employee at an automotive supplies store, possibly Western Auto in downtown Hill Valley, as Elsie mentioned to her husband Otis that “his [batteries] are expensive”, but that they could buy a new four-year battery at Sears for $14.95. Although Otis considered this far too expensive, he agreed to leave the money so Elsie could go and buy one.