1997 Mazda MX3 Changing battery

Hi. I need to change the battery in a Mazda ( I have done this numerous times in other cars I've had) but with the Mazda the a very long metal bar which runs all the way across the engine. It also is over the battery. I thought I would try and remover the said bar but cannot unscrew the bolts at all. Have you any suggestions. Keep in mind that there is very limited space to move the old battery, so it's not a case of being able just to unscrew the battery and lift it out. Have you come across this before and do you have any suggestions?