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Lithium Ion batteries have a shelf life not too different from their life in regular use. About 4 years is the accepted answer.
 
I have a couple things I have never opened from years ago...

Wow Cybergypsy I sure wish I was rich like you where I could just buy computers and never open them and just sit them in the closet. :D

All joking aside, why would you buy things and never open them for years? That's just money down the drain.
 
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