It's very difficult to determine the life of the battery in terms of number of years. I've seen ten year old battery perform decently vs. three month old battery going dead. Best practice would be to alternate each battery say, every month so that they do not go into Deep Discharge State or Over Use/Charge State wherein it would be very difficult to make the battery work. It's the chemicals in each cell of the battery that determine the overall state of the battery. Go ahead and buy a spare battery when you can but make sure that you use all of your batteries regularly. By the way, new Apple Notebooks have a built in battery. It makes no sense to buy a built in battery spare if there is no easy way to replace it.

• Answered by DD from Dubai
• Dec 3, 2009
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