GM adds week to Volt plant's usual summer closure Associated Press Copyright 2012 Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed. Updated 09:16 a.m., Monday, April 2, 2012 GM has already shut the plant from March 19 through April 23, as the supply of Volts grew on dealer lots. The Volt can travel about 35 miles on battery power before a small gas engine kicks in to generate electricity and keep the car going. [...] March, sales of the car were disappointing. A 60-day supply is considered optimal to keep a good selection of cars on dealer lots.