I found myself fixing shelf battens to old walls for someone. They only required two supporting battens at each end of each shelf. The job took much longer than expected. Why? The Victorian house walls on which the battens were fixed were crumbling underneath the plaster. This severely hindered the normal process of drilling holes, tapping in wall anchors and screwing in screws.
NOTE: This work required an assistant to provide another pair of hands to hold pieces of timber in place from time to time.