you can replace the battery yourself,remove the fuse from the spur unit that feeds the panel(if it has one,if not turn the mains power off at the consumer unit,sorry fuse box)now open the panel,remove the red and black wires from the battery,get yourself a new one same as old one,replace the wires on the battery,red to red,black to black terminals on battery,refit the cover,turn mains power on,reset the panel,now you have sorted it out,take a bow :-)
gts, January 2013