In principle, no battery can be stored without
loss of energy, although some battery systems may be stored for
longer periods of time than others. Processes inherent to the
battery's electrochemical system cause a gradual, but unavoidable
loss of usable energy which, however, is predictable. The best known
process is "self-discharge". This generally has to do with the
electrolytic solubility of the positive electrode material or its
thermodynamic instability (e.g. spontaneous decomposition).
Self-discharge in rechargeable batteries (secondary batteries,
accumulators) is particularly high in comparison to primary
batteries. At room temperature the rate of self-discharge is in the
range of 15% to 25% per month, depending on the system.
Electrochemical self-discharge in primary batteries is considerably
lower, and may even be below 2% per year at room temperature.
However, various processes take place in parallel with this which
lead to an increase of the battery's internal resistance during
storage. These processes lead to a reduction in load capability.
Loss of usable energy becomes noticeable only at relatively high
discharge rates (e.g. motor applications, flashlights etc.). This
effect, however, has nothing to do with self-discharge. At low
discharge rates the increased internal resistance which occurred
during storage will not be detectable.
Under normal storage conditions, the following approximate values
apply to self-discharge.
| Battery Type |
Self-discharge |
| Alkaline-manganese round cells |
max. 2%/year |
| Zinc round cells |
max. 4%/year |
| Rechargeable (dependent on system) |
10% to 25%/month |
|
|
