rear brakes occasionally will get hot and smoke?

What is your question?

Especially on longer trips,(100 miles>) they appear to be hanging up enough to smoke. New pads were put on with no results. Another mecanic, many yrs exper./w/colledge on auto.repair also, could not find a problem. took wheels off, check calipers ect., took on two road test, checked system from front to back and found nothing. The vehicle has 90 thou. and the last time battery light came on? might have nothing to do with it. hasn,t come on again. any suggestions? Thanks