I've managed to do this so thought I'd post how I did it in case anybody else has the same problem. The mistake I was making was that I was trying to remove the whole front of the unit not realising that there are 2 separate compartments to the underside of the unit.
There are two separate battery compartments which you access from the bottom of the unit. There is no need to remove the front where the lcd display is. All you have to do is remove the screw and then access the battery compartment to the left of the screw, replace 2 batteries and then do the same to the battery compartment to the right of the screw.
Joolz, October 2012
