Heat Damage

• Exposure to extreme temperatures will reduce the battery life of your iPod more than any other factor. If you store the device in temperatures below - 4 degrees Fahrenheit or higher than 113 degrees, permanent damage to the battery can occur that will negatively affect its ability to hold a charge. Ideally, your iPod should be stored close to room temperature, which is 72 degrees Fahrenheit, according to Apple.
  
  

Lack of Use

• iPods have lithium-ion batteries, which require relatively frequent use in order to maintain their ability to hold a charge. When your iPod is in operation, electrons move around in the device's battery -- when the electrons are not stimulated often enough the battery suffers. If you have not been charging your iPod completely and then running down the battery at least once a month, the battery may not hold the charge it was designed to.
  
  

Age

• According to Apple, the iPod battery is designed to keep up to 80 percent of its original capacity for the first 400 charge cycles. One cycle consists of a full charge and subsequent complete depletion of the battery. After that, the iPod battery will naturally lose its ability to keep a charge over time until it is no longer able to operate.
  
  

Replacement

• If your iPod battery fails to hold at least 50 percent of its original charge capacity during the first year after purchase, Apple will replace the battery as defective at no cost. If you purchased the extended protection plan for your device, the coverage lasts for two years. After that time, the battery will be replaced at a fee. In all cases, Apple recommends careful disposal of the old battery -- always check with your local waste disposal company to determine the safest way to throw away the battery if you elect to change it yourself.