There has been significant progress in the technology development of batteries adopted in electric vehicles (EV) and hybrid electric vehicles (HEV): in addition to the increased energy density, the battery can be recharged for thousands of times. With an adequate utilization of these technology breakthroughs by engineers, EV and HEV are provided with an edge to compete with traditional vehicles in terms of cost, reliability and lifespan.
The definition of battery capacity is the electricity the battery sustains from full charge to zero charge. Putting the battery in either full charge or zero charge will drastically reduce the lifespan of it; hence, the battery status should be monitored deliberately in order to prevent it from being in neither of the ends. Compared to a battery which works in the status from 70% to 30% (40% of the battery capacity), the recharge cycles of a battery which work in the status from 90% to 10% (80% of the battery capacity) can be decreased by 3 times.
To strike a balance between battery capacity and battery lifespan has been a challenge for battery system engineers. With the conditions (40% and 80% of the battery capacity) mentioned above taken into account, if the exercisable battery capacity is restricted to 40%, then the battery lifespan can be prolonged by 3 times. However, the battery size also has to be doubled in order to obtain the same capacity of a battery whose exercisable battery capacity is set to 80%. In that case, the weight and size of the battery will be doubled, which results in a cost increase and a decrease in efficiency.
In general, car manufacturers adopt batteries whose lifespan goes up to over 10 years and have specific demands in regard to the exercisable capacity of the batteries. The current challenge the battery system engineers are facing is to achieve the maximum capacity with the smallest battery possible. In order to attain the goal, a deliberate management of battery by the electronic circuit is required.
