Reuters: Republican John McCain said on Monday if elected president he would challenge American experts to develop a futuristic battery to power cars and win a US$300 million prize. McCain, a week after taking heat from Democrats for reversing his stance on offshore oil drilling after long opposing it, sought to portray himself as a forward-looking leader on solving America’s energy crisis. With Americans reeling from record-high US$4-a-gallon gasoline during the prime summer driving …