Question

What happens to the capacity of a battery as it is cycled over a year (charge / discharge)?
Why are higher voltages needed to recharge a battery with age?

Answer 1

As the battery is charged and discharged, over a year, the capacity of the battery reduces. This is because of the following reason. During charging and discharging( using up of the battery) the ions move freely between the cathode and the anode of the battery. In the charging part of the cycle, ions move from cathode to the anode. During discharging i.e. using the battery cycle, ions flow from anode to cathode which is the reverse flow. Over a peiod of time, this process wears out the cathode.And less ions move between the anode and the cathode, thus reducing the capacity of the battery to discharge for a longer period.

Over a period of time, the batteries tend to increase their internal resistance. We know the basic Ohm's law i.e. V = IR. Clearly as the resistance increases, the Voltage required to deliver the same amount of current increases.