What Is a Battery Pack?
A battery pack consists of a number of single cells connected together to form a single pack.
A battery pack of various voltages and capacities can be made by connecting different numbers of cells in different ways.
In addition, the size, shape, and terminal position can be customized freely to suit the application. Usually packaged in heat-shrinkable tubing, they are also available in metal cases or resin.
Uses of Battery Packs
Battery packs can be freely designed in terms of shape, voltage, and capacity to suit a variety of applications. The original cells for battery packs include nickel-cadmium, nickel-metal hydride, and lithium-ion batteries, each of which has different characteristics, and can be selected according to the intended use.
Although nickel-cadmium batteries have long been used in a variety of devices, nickel-metal hydride batteries with higher capacity and lower self-discharge have recently become mainstream. Lithium-ion batteries have safety issues such as heat generation and ignition, but their lightweight and high capacity have led to their use mainly in portable devices.
Principle of Battery Packs
Battery packs come in a variety of shapes and sizes, depending on how the cells are arranged. The main types are the S array, in which cylindrical cells are arranged horizontally, and the W array, which has multiple rows of S array cells. Also, the L array, in which cells are arranged vertically, and the E array, which has multiple rows of L array cells. The output voltage can be increased by connecting the arrayed cells in series, and the capacity can be increased by connecting them in parallel. Furthermore, by combining cells in series and parallel, battery packs of desired voltage and capacity can be created.
The capacity of battery packs is expressed in units of mAh or Ah. For example, 1Ah has the capacity to carry a current of 1A for 1 hour. The ratio of the actual charge to this capacity is the charge rate (SOC). For example, nickel-metal hydride batteries should be used with a charge rate between 25% and 75%, and lithium-ion batteries should be used with a charge rate between 10% and 90% to extend the cycle life of the battery. There is also a depth of discharge (DOD) index that indicates the ratio of discharged to capacity, and repeated use at shallower depths of discharge is usually said to extend service life.
Most battery packs have a controller that controls charging and discharging together. To prevent unevenness in the state of charging and discharging due to variations in the characteristics of individual cells, the controller controls charging and discharging for each cell and for safe, rapid charging.