What makes primary batteries leak on very deep discharge?

Question

From my experience, if a primary (alkaline or zink) battery is left in a device with very low consumption (like a remote control, or a quartz watch) then at some point all the energy is drained and later the battery electrolyte leaks and damages the device.

What exactly makes batteries leak on very deep discharge? Do all primary batteries behave this way?

Answer 1

In the case of the carbon-zinc cell, the case of the cell is one of the electrodes. The process of generating electricity uses up the zinc, so it corrodes from the inside out. Eventually holes will develop, and the electrolyte can leak out.