What are battery manufacturers doing to prevent damage from overcharging?
Quite a lot. The demand for rapid charging has lead to a great increase in overcharging abuse. Most all NiCd cells can be rapid charged. The trick is to stop charging when it is fully charged. The so called “rapid charge” type of cells just incorporate protection against overcharging at high currents. Most often, this is done with activated carbon inserted in the cell to promote the collection of oxygen and to deliver it to the cathode for recombination. By increasing the rate of oxygen transport, one is increasing the ability of the cell to resist venting. Note however, that heat is still generated. The price one pays for this is reduced capacity. Everything takes space in the cell, and space for carbon means less space for active material. Also, there have been some indications that carbon can cause the cadmium metal to corrode, possibly leading to a shorter life.