There are times when I try to merge all chunks in 1 step, it fails due to 'not enough memory' error. However, if I stage the merge so that I join chunks 1 and 2 to create chunk 6, then merge chunk 3 and 6 to form 7, then merge chunk 4 and 7 to create 8.. etc, I have sufficient memory.
This is a slow process and one that would be much improved by adding a "Batch join by stages" option to the batch process dialogue.
Thanks.