Glyn - I started my testing last night but quickly found this was a 4GB image instead of the 8GB image discussed here: Increase emonSD pre-built SD card to 8GB min
I had been writing (trying to write?) a migration script that captures the items not grabbed by the backup/export script. And I quickly ran out of space on the /data directory:
/dev/mmcblk0p3 194M 37M 147M 21% /home/pi/data
Is it possible to create the 8GB image instead?