Majority of the people feel that it is a cold season that damages and shortens battery life while actually, it is the heat which causes major battery problems. Heat makes battery fluid vaporize, causing damage to the structure of the battery.
Overcharging also badly affects battery life; this is usually because of a flaw in a component of the charging system. Overcharging is actually a slow killer of the battery.
It is, however, true, that there are more people complaining about their batteries in winters than in colder weathers. It is due to the slow electrochemical action that provides the battery with its power. The thickness of the engine oil also increases, which makes the engine harder to turn over. All these factors combined definitely cause lots of battery and starting trouble.