Overcharging and potential plate failure:

As the battery operating temperature increases, battery internal resistance decreases and the charge rate acceptance of the battery increases accordingly. That is, as temperature increases, the charging voltage applied by the alternator to a battery must be reduced to avoid overcharging. The following curve indicates the variation of voltage with temperature that should be applied to a lead-acid battery for adequate and correct charging.
 
At elevated under-bonnet temperatures, charging voltage control can be difficult and inadequate, resulting in extended overcharging and reduced battery life due to positive plate material degradation and loss, often accompanied by softening of the negative plate material. Different rates of air ventilation and the position of the battery in the engine bay can lead to an internal material difference in alternator and electrolyte temperatures which increases the rate of overcharging the battery receives and the subsequent gassing.

At elevated temperatures, the discharge capacity of a battery is increased, and the

ability to deliver higher cranking current is increased - as shown in the following graphs. In practical terms, this is of no real advantage, except in the case of a worn or reduced capacity battery, which may still function adequately due to the elevated temperatures.  
This masks the fact the battery is nearing its end-of-life and when the temperatures become colder and the engine requires higher cranking amps to turn over due to the engine oil becoming viscous, the battery ultimately fails suddenly.  

All automotive lead-acid batteries slowly lose charge when not in service. This is known as self-discharge. The rate of self-discharge increases with increasing temperature. The time batteries can be allowed to stand without recharging is reduced with increasing temperature of storage. Batteries should be recharged when the Open Circuit Voltage drops to 12.4 volts.