If you have the non tilting seats, back rake adjustment only fitted on the 4 seat cars originally, then you will not have the clearance to remove the battery through the rear bulkhead unless you remove a seat. I suspect that is why you have no access panel. However if your seat backs do tilt forward then I can't see why an access panel cannot be fitted. The alloy cover panel when fitted is held in with 6 screws and as John said position is critical to avoid contacting anything behind. The six screws are in fact a total faff and if you use 6mm hex socked door bolts fitted from the rear, two only required, you can then use alloy thumb nuts, one each side for a faster access. I have cut a piece of 4mm closed cell foam which is stuck to the rear of the alloy closer plate and fits exactly the cut out in the rear bulkhead and where the plate edges sit on the ply bulkhead I have used 2mm foam to prevent rattles and act as a seal. If it turns out that your battery has to come out from the rear then you will need to jack the rear of the car up by jacking from a central point on the rear chassis double skinned cross member. I then position axel stands on the outer edges of the cross member just forward of the front wheels and remove the jack for work space. DO CHOCK THE FRONT WHEELS! remember the handbrake works on the rear wheels! Do you have a tool tray, if so remove that, small screws, and you can work through the top to disconnect everything and lift the battery out and lower it to the ground! Whatever the outcome whilst working there fit the fused Ctek charging adaptor so you can maintain the new battery!
