WASHINGTON — The United States Postal Service plans to make at least 40% of all new delivery vehicles battery electric, including at least 50% of the trucks purchased from Oshkosh Corp. The move marks an increase from its previous plan to make only 20% of its new vehicles electric as part of a $2.98 billion effort to begin replacing its 30-year-old fleet. In addition to the 50,000 new vehicles purchased from Oshkosh, the Postal Service plans to buy 34,500 “off-the-shelf” vehicles over the next two years “because of the critical and immediate need to accelerate the replacement of our aging flee…