Overcharging – continuing the charging of a battery even after it has reached 100% capacity / State of Charge or supplying more energy to a battery than it can convert into stored energy over a given period of time.
What’s actually happening during the charging process? Electrical energy is being passed through the battery causing chemical changes inside. In a lithium ion battery, for example, the electrical current causes the lithium ions to move from the positive cathode to the negative anode. Doing so uses up some of the energy being put into the battery by the charger.
Overcharging can occur in two ways:
- The energy being past through the battery is too strong.
- Energy is being past through the battery when it is fully charged.
Over charging during charging
Charging is generally a slow business. The electro-chemical reaction inside a rechargeable battery can only happen at a certain rate and every battery chemistry is different. Some of the latest lithium ion chemistries can turn electrical current into stored energy much faster than lead acid models but they still have their limits.
Turn up the current going through a battery and you don’t speed up the charge, you just push in more energy than the battery can handle and so it turns it into heat. Heat can damage internal components or in extremes cause the battery to explode.
Over charging a fully charged battery
When the battery is fully charged, but still has current being passed through it, the unit has nothing to do with this energy from the charger and so it starts turning the energy into heat. As with over charging during charging its the heat which damages a battery by either causing the electrolyte to ‘boil away’ (often as gases through safety vents) and/or warping the anode and cathode plates.
Avoiding overcharge
Use the right charger for the right battery type – different battery chemistries have different charging patterns. Some need a stronger current when a battery is flat and then a lower current later. Others work best with a constant current. As such connecting the wrong charger to the wrong battery type can lead to overcharging.
Use a quality smart charger – Modern quality chargers monitor a number of factors such as the battery voltage and the temperature of the cells in order to ascertain when a battery is fully charged. By doing so they can find the correct charge voltage (not the stated voltage) ensuring the product really is fully charged without causing damage.
Older or budget chargers don’t recognize all these signals and so tend to be a false economy, because they shorten the lives of the batteries they charge. You may save on the charger, but you lose on the costs of replacing batteries that could have lasted much longer.
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