Although the average life of car batteries has increased to 42 months under normal operating conditions, a battery’s life can be reduced by factors involving storage, vibration, temperature conditions, overcharging and cycling.
Batteries have a limited shelf life and when stored gradually lose their power to perform. On average, a fully-charged battery takes about 13 weeks to gradually discharge to less than its optimum operating level. The rate of charge loss depends on battery type (low maintenance or maintenance free) and temperature conditions.
Charge loss becomes more evident when temperatures increase. At 20C low maintenance batteries lose approximately one half of one percent of charge per day (30 percent in 60 days). At 30C charge loss is usually double the rate for 20C.
Under similar temperature conditions, maintenance free batteries lose their charge more slowly than low maintenance batteries. Excessive humidity will also accelerate charge loss. Batteries stored upright in cool and dry conditions is ideal.
Whilst in storage batteries have not been recharged and allowed to go flat, may be permanently damaged. Recharging every four to eight weeks, depending on storage conditions, will restore batteries to “as new” condition.
Vibration loosens active material from the battery plates which may cause shorting and can also damage the structural integrity of battery connections.
Overcharging permanently damages batteries, therefore overcharging corrodes the grid mesh and accelerates loss of active material from the positive plate. It also deteriorates separators and increases water loss.
A higher temperature requires higher charge rates which leads to an accelerated loss of active material from the positive plates, as well as separator deterioration, increased grid corrosion and water loss.
Charging and recharging causes expansion and contraction of positive active material which leads to increased shedding. The depth and frequency of discharge influences the amount of deterioration.
Sulphation occurs when a battery is stored over a long period of time in a state of low charge. The crystalline structure of the discharged active material, (lead sulphate), is gradually transformed into a substance which resists recharge, causing permanent deterioration.
This article is found in the Virtual mechanic CD Rom
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By Darren Gow-Brown, Melbourne Australia