Basics of Battery Storage

It's occasionally necessary to keep batteries in storage. Unfortunately, any battery will age while in storage, but taking some basic steps can help prolong the life of a battery while storing it. Of course, one of the factors that can age a battery the quickest is exposure to temperature extremes. The ideal storage temperature for most batteries is 59°F, and keeping batteries in near-range of this temperature ideal will help prolong their life sufficiently. Additionally, lithium-ion batteries are also exposed to temperature extremes frequently, when units are left out in the sun or overcharged. Remembering to keep cell phones and laptops out of the sun, and unplugged when fully charged, will go a long way toward prolonging their batteries' lives. Here are some tips that Battery University suggests for prolonging the life of batteries in storage:

Simple Guidelines for Storing Batteries

• Primary batteries store well. Alkaline and primary lithium batteries can be stored for 10 years with moderate loss capacity.
   
• Remove battery from the equipment and store in a dry and cool place.
   
• Avoid freezing. Batteries freeze more easily if in discharged state.
   
• Charge lead acid before storing and monitor the voltage or specific gravity frequently; apply a boost if below 2.10V/cell or an SG below 1.225.
   
• Nickel-based batteries can be stored for five years and longer, even at zero voltage; prime before use.
   
• Lithium-ion must be stored in a charged state, ideally 40 percent. This assures that the battery will not drop below 2.50V/cell with self-discharge and fall asleep.
   
• Discard Li-ion if the voltage has stayed below 2.00/V/cell for more than a week.

 Sources:

How to Store Batteries