(1) Capacity maintenance
Fully-charged battery after long-term storage, the capacity of which will become less and less, is in a state of discharge, which is called self-discharge. Even unused battery cannot avoid this. Self-discharge is caused by battery internal chemistry reaction and electrochemistry reaction.
- Chemistry aspect
The active materials in positive(PbO2) or negative(Pb) will decompose or react to sulphuric acid(electrolyte) to become PbSO which is more stable. That is called self-discharge.
- Electrochemistry aspect
Due to the impure materials, local circuit will be formed inside the battery or oxidation-reduction reaction will take place in the positive pole and the negative pole, which will arouse self-discharge. The self- discharge electric quantity of VRLA battery is very small. It is one third to one fourth the quantity of the common lead acid battery. That is because battery has a strong ability of capacity maintenance. Picture 1 shows the relations between the ability of capacity maintenance and storage condition.
figure 1 the ability of capacity maintenance, recharge and storage condition
(2) Storage
The capacity of recharged lead acid battery will be affected after long term storage. But lead –calcium battery has a longer period of storage than traditional lead acid battery. Battery needs to be charged during storage. The interval of charge is given in figure 1
Figure 1 storage temperature and recommended interval of charge
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Storage temperature
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Recommended Interval of charge
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Method of charge
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Below 20oC(68oF)
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Every 6 months
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Constant voltage charging 2.275V/cell 16-24 hours
Constant voltage charging 2.45V/cell 5-8 hours
Constant current charging 0.05CA 5-8 hours
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20-30oC(68-86oF)
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Every 3 months
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Over30oC(86oF)
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No storage
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Although the method of charge is no more than constant voltage charge or constant current charge, most of the time capacity cannot reach 100% after the battery is charged. Therefore, battery needs charging and discharging many times.
(3) Open circuit voltage and residual capacity
Figure 12 shows the relations between open circuit voltage and residual capacity.
Figure 12 characteristic of open circuit
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