Lithium based batteries require extra attention as improper storage can cause units to overheat and potentially catch fire in a process known as thermal runaway. Many types also have both the negative and positive terminals on the same side making it easy to accidentally short out the unit on metal shelving if they are left uncovered.
This article relates to both Lithium batteries (also known as Lithium Metal non rechargeable) and Lithium Ion batteries (rechargeable) that are to be stored for several weeks or longer.
The higher the temperature the faster the battery will self-discharge but this is not an issue in itself so long as the correct State of Charge is maintained (see below). Temperatures below freezing will not damage Lithium batteries as they contain no water but they should be bought to above freezing before charging or usage to avoid damage.
The main issue with humidity is that condensation can build up between the terminals and in very wet conditions cause a short which could cause the battery to overheat and even catch fire. As an extra safety precaution the terminals should always have separate covers.
All batteries gradually self-discharge even when in storage. A Lithium Ion battery will self-discharge 5% in the first 24 hours after being charged and then 1-2% per month. If the battery is fitted with a safety circuit (and most are) this will contribute to a further 3% self-discharge per month.
Lithium batteries should be kept at around 40-50% State of Charge (SoC) to be ready for immediate use – this is approximately 3.8 Volts per cell – while tests have suggested that if this battery type is kept fully charged the recoverable capacity is reduced over time. The voltage of each cell should not fall below 2 volts as at this point the anode starts dissolving causing copper shunts to form which will cause an irreversible loss of capacity. Similarly lithium based batteries can be damaged by over charging which causes the cathode to decompose.
When checking the voltage make sure the battery has not been charged or discharged recently, is at room temperature throughout and has been in a vibration free environment. The best way to do this is to rest the battery at room temperature for at least an hour and a half.
If a Lithium Ion battery is heavily discharged an attempt to recover it can be made using the following steps:
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The following guidance is based on batteries that are kept at the right temperature, the right humidity and in the correct State of Charge. Under these conditions standard lithium based batteries can have a shelf life of up to ten years. Military and Medical lithium based batteries can have a shelf life of up to twenty plus years.
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