Batteries are a perishable product and start
deteriorating right from the time they leave the manufacturing
plant. For this reason, it is not advisable to stock up on
batteries for future use. This is especially true with lithium-based
batteries. The buyer should also be aware of the manufacturing
date. Avoid acquiring old stock.
batteries in a cool and dry storage area. Refrigerators are
recommended, but freezers must be avoided because most battery
chemistries are not suited for storage in sub-freezing temperatures.
When refrigerated, the battery should be placed in a plastic
bag to protect it against condensation.
The NiCd battery can be stored unattended for
five years and longer. For best results, a NiCd should be
fully charged, then discharged to zero volts. If this procedure
is impractical, a discharge to 1V/cell is acceptable. A fully
charged NiCd that is allowed to self-discharge during storage
is subject to crystalline formation (memory).
Most batteries are shipped with a state-of-charge
(SoC) of 40 percent. After six months storage or longer,
a nickel-based battery needs to be primed before use. A slow
charge, followed by one or several discharge/charge cycles,
will do. Depending on the duration of storage and temperature,
the battery may require two or more cycles to regain full
performance. The warmer the storage temperature, the more
cycles will be needed.
The Li-ion does not like prolonged storage.
Irreversible capacity loss occurs after 6 to 12 months,
especially if the battery is stored at full charge and at
warm temperatures. It is often necessary to keep a battery
fully charged as in the case of emergency response, public
safety and defense. Running a laptop (or other portable device)
continuously on an external power source with the battery
engaged will have the same effect. Figure 15-1
illustrates the recoverable capacity after storage at different
charge levels and temperatures.
The combination of a full charge condition and
high temperature cannot always be avoided. Such is the case
when keeping a spare battery in the car for a mobile phone.
The NiMH and Li-ion chemistries are most severely affected
by hot storage and operation. Among the Li-ion family,
the cobalt has an advantage over the manganese (spinel) in
terms of storage at elevated temperatures.
(recommended storage charge level)
(typical user charge level)
|| 98% after 1 year
|| 94% after 1 year
|| 96% after
|| 80% after
|| 85% after 1 year
|| 65% after 1 year
|| 75% after
|| 60% after
Figure 15-1: Non-recoverable capacity
loss on Li-ion batteries after storage.
High charge levels and elevated
temperatures hasten the capacity loss. Improvements in chemistry
have increased the storage performance of some Li-ion batteries.
The recommended storage temperature of a lithium-based
battery is 15°C (59°F) or less. A charge level of 40 percent
allows for some self-discharge that naturally occurs; and
15°C is a practical and economical storage temperature that
can be achieved without expensive climate control systems.
While most rechargeable batteries cannot be stored
at freezing temperatures, some newer commercial Li-ion
batteries can be kept at temperatures of -40°C without apparent
side effects. Such temperature tolerances enable long and
cost-effective storage in the arctic.
The SLA battery can be stored for up to two years
but must be kept in a charged condition. A periodic topping
charge, also referred to as ‘refreshing charge’, is required
to prevent the open cell voltage from dropping below 2.10V.
(Depending on the manufacturer, some lead acid batteries may
be allowed to drop to lower voltage levels). When self-discharged
below a critical voltage threshold, sulfation occurs on most
lead acid batteries. Sulfation is an oxidation layer on the
negative plate that alters the charge and discharge characteristics.
Although cycling can often restore the capacity loss, the
battery should be recharged before the open cell voltage drops
The SLA cannot be stored below freezing temperatures.
Once a pack has been frozen, it is permanently damaged and
its service life is drastically reduced. A previously frozen
battery will only be able to deliver a limited number of cycles.