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Automobile battery pack consisting of 28 Optima Yellow Tops

A battery pack is a set of any number of (preferably) identical batteries or individual battery cells.[1][2] They may be configured in a series, parallel or a mixture of both to deliver the desired voltage, capacity, or power density. The term battery pack is often used in reference to cordless tools, radio-controlled hobby toys, and battery electric vehicles.

Components of battery packs include the individual batteries or cells, and the interconnects which provide electrical conductivity between them.[3] Rechargeable battery packs often contain voltage and temperature sensors, which the battery charger uses to detect the end of charging.[4] Interconnects are also found in batteries as they are the part which connects each cell, though batteries are most often only arranged in series strings.

When a pack contains groups of cells in parallel there are differing wiring configurations which take into consideration the electrical balance of the circuit. Battery Management System are sometimes used for balancing cells in order to keep their voltages below a maximum value during charging so as to allow the weaker batteries to become fully charged, bringing the whole pack back into balance.[5] Active balancing can also be performed by battery balancer devices which can shuttle energy from strong cells to weaker ones in real time for better balance.[5] A well-balanced pack lasts longer and delivers better performance.[6][1]

For an inline package, cells are selected and stacked with solder in between them. The cells are pressed together and a current pulse generates heat to solder them together and to weld all connections internal to the cell.

Calculating state of charge

SOC, or state of charge, is the equivalent of a fuel gauge for a battery. SOC cannot be determined by a simple voltage measurement, because the terminal voltage of a battery may stay substantially constant until it is completely discharged. In some types of battery, electrolyte specific gravity may be related to state of charge but this is not measurable on typical battery pack cells, and is not related to state of charge on most battery types. Most SOC methods take into account voltage and current as well as temperature and other aspects of the discharge and charge process to in essence count up or down within a pre-defined capacity of a pack.[7][8] More complex state of charge estimation systems take into account the Peukert effect which relates the capacity of the battery to the discharge rate.[9]


An advantage of a battery pack is the ease with which it can be swapped into or out of a device. This allows multiple packs to deliver extended runtimes, freeing up the device for continued use while charging the removed pack separately.

Another advantage is the flexibility of their design and implementation, allowing the use of cheaper high-production cells or batteries to be combined into a pack for nearly any application.

At the end of product life, batteries can be removed and recycled separately, reducing the total volume of hazardous waste.


Packs are often simpler for end users to repair or tamper with than a sealed non-serviceable battery or cell. Though some might consider this an advantage it is important to take safety precautions when servicing a battery pack as they pose a danger as potential chemical, electrical, and fire risks.

See also


  1. ^ a b Hassini, Marwan; Von Hohendorff Seger, Pedro; Redondo-Iglesias, Eduardo; Pelissier, Serge; Venet, Pascal (27 October 2023). "Capacity Dispersion and Impact of Outliers in a Second Life Battery". IEEE VPPC 2023. Milan, Italy.
  2. ^ Li, Wei; Garg, Akhil; Xiao, Mi; Peng, Xiongbin; Le Phung, My Loan; Tran, Van Man; Gao, Liang (2020-10-10). "Intelligent optimization methodology of battery pack for electric vehicles: A multidisciplinary perspective". International Journal of Energy Research. 44 (12): 9686–9706. Bibcode:2020IJER...44.9686L. doi:10.1002/er.5600. ISSN 0363-907X.
  3. ^ Harper, Gavin; Sommerville, Roberto; Kendrick, Emma; Driscoll, Laura; Slater, Peter; Stolkin, Rustam; Walton, Allan; Christensen, Paul; Heidrich, Oliver; Lambert, Simon; Abbott, Andrew; Ryder, Karl; Gaines, Linda; Anderson, Paul (6 November 2019). "Recycling lithium-ion batteries from electric vehicles". Nature. 575 (7781): 75–86. Bibcode:2019Natur.575...75H. doi:10.1038/s41586-019-1682-5. ISSN 1476-4687. PMID 31695206.
  4. ^ Simpson, Chester (1995). "Battery charging" (PDF). National Semiconductors.
  5. ^ a b "Battery balancing methods: A comprehensive review | IEEE Conference Publication | IEEE Xplore". doi:10.1109/VPPC.2008.4677669. S2CID 42399871. Retrieved 2024-01-19.
  6. ^ Duraisamy, Thiruvonasundari; Kaliyaperumal, Deepa (2020-06-01). "Active cell balancing for electric vehicle battery management system". International Journal of Power Electronics and Drive Systems (IJPEDS). 11 (2): 571. doi:10.11591/ijpeds.v11.i2.pp571-579. ISSN 2722-256X.
  7. ^ "Battery state-of-charge estimation | IEEE Conference Publication | IEEE Xplore". doi:10.1109/ACC.2001.945964. S2CID 57885701. Retrieved 2024-01-19.
  8. ^ Hassini, Marwan; Redondo-Iglesias, Eduardo; Venet, Pascal (19 July 2023). "Lithium–Ion Battery Data: From Production to Prediction". Batteries. 9 (7): 385. doi:10.3390/batteries9070385. ISSN 2313-0105.
  9. ^ "State of charge (SoC) estimation on LiFePO4 battery module using Coulomb counting methods with modified Peukert | IEEE Conference Publication | IEEE Xplore". doi:10.1109/rICT-ICeVT.2013.6741545. S2CID 5621134. Retrieved 2024-01-19.