A good battery with an adequate charge is absolutely essential for reliable cold starting. A weak battery or one that is run down may not deliver enough amps to crank the engine when temperatures plunge and the oil thickens. Cold weather can be hard on batteries, but so can hot weather because it increases water loss from the electrolyte inside the battery. That’s why batteries in hot climates usually don’t last as many years as those in more moderate or colder climates.

The battery must also be capable of providing backup power for the vehicle’s electrical accessories and electronic modules. When the engine is running, the charging system can usually produce enough current to meet all of the vehicle’s electrical needs. But when the engine is idling and the lights, heater, defroster, radio or other accessories are placing high loads on the system, additional power may be drawn from the battery if the alternator can’t produce enough juice. And when the key is off, the battery has to provide a steady supply of voltage to any onboard modules or other accessories that need power.

When a battery is disconnected or goes completely dead, the loss of voltage can cause a variety of problems. Radio presets and memory seat/mirror settings are lost, and so are the adaptive and learned memories in the PCM and other modules. The PCM can forget fault codes and other diagnostic information (...