We set the spec at 16GB because, to be honest, we didn’t test anything above that. The V5 can only read and write to SD Cards formatted with the FAT32 file system, we have found a few “off brand” cards that don’t work and we don’t really know why.
Perhaps we can get a list of known good cards going in this topic, The two I have here on my desk are.
Kingston 4GB, 1415PX5044P
Sandisk 16GB, Extreme Pro,