It is widely believed that cold temperatures were bad for battery life. The exact opposite is true. High temperatures, or a faulty component in the charging system are bigger culprits.
When temperatures outside reach 90 degrees, the temperature under a car's hood
reaches upward of 140 degrees. That's weight loss success story temps. Heat causes car battery fluid to evaporate and that can damage the internal structure of the battery as well as speed up car battery corrosion. Specifically, if a component malfunctions in the charging system, that can force the battery to charge at too high of a rate year round.
Adding to the strain on car batteries in summer months is the frequent use of
various electronic devices by many drivers. Devices like satellite radios, GPS
systems, portable DVD players and radar detectors are plugged in or in some
cases hardwired to the electrical system all of which add stress to car