Ford Cougar Battery Problems

eratic speedo, sometimes dropping to zero then back to normal - does not affect rev counter, but does to radio volume. engine kangaroos - garages cant seem to find fault

over the past few months my remote key fob has become more and more innefective and now it hardly works at all.I have changed the battery with no success and re-set the 'cycle'again with no success.This happens on all the doors.I sometimes ...