mobile | classic
Dataweek Electronics & Communications Technology Magazine

Follow us on:
Follow us on Facebook Share via Twitter Share via LinkedIn


Electronics Buyers' Guide

Electronics Manufacturing & Production Handbook 2017


Series and parallel battery configurations
21 February 2018, Power Electronics / Power Management

Batteries achieve the desired operating voltage by connecting several cells in series; each cell adds its voltage potential to arrive at the total terminal voltage. Parallel connection attains higher capacity by adding up the total ampere-hour (Ah).

Some packs may consist of a combination of series and parallel connections. Laptop batteries commonly have four 3,6 V Li-ion cells in series to achieve a nominal voltage 14,4 V, and two in parallel to boost the capacity from 2400 mAh to 4800 mAh. Such a configuration is called 4S2P, meaning four cells in series and two in parallel. Insulating foil between the cells prevents the conductive metallic skin from causing an electrical short.

Most battery chemistries lend themselves to series and parallel connection. It is important to use the same battery type with equal voltage and capacity (Ah) and never to mix different makes and sizes. A weaker cell would cause an imbalance. This is especially critical in a series configuration because a battery is only as strong as the weakest link in the chain. An analogy is a chain in which the links represent the cells of a battery connected in series (Figure 1).

Figure 1: Comparing a battery with a chain.
Figure 1: Comparing a battery with a chain.

A weak cell may not fail immediately but will get exhausted more quickly than the strong ones when on a load. On charge, the low cell fills up before the strong ones because there is less to fill and it remains in over-charge longer than the others. On discharge, the weak cell empties first and gets hammered by the stronger brothers. Cells in multi-packs must be matched, especially when used under heavy loads.

Single-cell applications

The single-cell configuration is the simplest battery pack; the cell does not need matching and the protection circuit on a small Li-ion cell can be kept simple. Typical examples are mobile phones and tablets with one 3,60 V Li-ion cell. Other uses of a single cell are wall clocks, which typically use a 1,5 V alkaline cell, wristwatches and memory backup, most of which are very low-power applications.

Series connection

Portable equipment needing higher voltages use battery packs with two or more cells connected in series. Figure 2 shows a battery pack with four 3,6 V Li-ion cells in series, also known as 4S, to produce 14,4 V nominal. In comparison, a six-cell lead acid string with 2 V/cell will generate 12 V, and four alkaline with 1,5 V/cell will give 6 V.

Figure 2: Series connection of four cells (4S).
Figure 2: Series connection of four cells (4S).

If you need an odd voltage of, say, 9,50 volts, connect five lead acid, eight NiMH or NiCd, or three Li-ion in series. The end battery voltage does not need to be exact as long as it is higher than what the device specifies. A 12 V supply might work in lieu of 9,50 V. Most battery-operated devices can tolerate some over-voltage; the end-of-discharge voltage must be respected, however.

Parallel connection

Figure 3: Parallel connection of four cells (4P).
Figure 3: Parallel connection of four cells (4P).

If higher currents are needed and larger cells are not available or do not fit the design constraint, one or more cells can be connected in parallel. Most battery chemistries allow parallel configurations with little side effect. Figure 3 illustrates four cells connected in parallel in a P4 arrangement. The nominal voltage of the illustrated pack remains at 3,60 V, but the capacity (Ah) and runtime are increased fourfold.

A cell that develops high resistance or opens is less critical in a parallel circuit than in a series configuration, but a failing cell will reduce the total load capability. It’s like an engine only firing on three cylinders instead of on all four. An electrical short, on the other hand, is more serious as the faulty cell drains energy from the other cells, causing a fire hazard. Most so-called electrical shorts are mild and manifest themselves as elevated self-discharge.

A total short can occur through reverse polarisation or dendrite growth. Large packs often include a fuse that disconnects the failing cell from the parallel circuit if it were to short. Figure 4 illustrates a parallel configuration with one faulty cell.

Figure 4: Parallel/connection with one faulty cell.
Figure 4: Parallel/connection with one faulty cell.

A weak cell will not affect the voltage but provide a low runtime due to reduced capacity. A shorted cell could cause excessive heat and become a fire hazard. On larger packs a fuse prevents high current by isolating the cell.

Series/parallel connection

The series/parallel configuration shown in Figure 5 enables design flexibility and achieves the desired voltage and current ratings with a standard cell size. The total power is the product of voltage times current; four 3,6 V (nominal) cells multiplied by 3400 mAh produce 12,24 Wh. Four 18650 energy cells of 3400 mAh each can be connected in series and parallel as shown to get 7,2 V nominal and 12,24 Wh. The slim cell allows flexible pack design but a protection circuit is needed.

Li-ion lends itself well to series/parallel configurations but the cells need monitoring to stay within voltage and current limits. Integrated circuits (ICs) for various cell combinations are available to supervise up to 13 Li-ion cells. Larger packs need custom circuits, and this applies to e-bike batteries, hybrid cars and the Tesla Model 85 that devours over 7000 18650 cells to make up the 90 kWh pack.

Figure 5: Series/ parallel connection of four cells (2S2P).
Figure 5: Series/ parallel connection of four cells (2S2P).

Terminology to describe series and parallel connection

The battery industry specifies the number of cells in series first, followed by the cells placed in parallel. An example is 2S2P. With Li-ion, the parallel strings are always made first; the completed parallel units are then placed in series. Li-ion is a voltage-based system that lends itself well for parallel formation. Combining several cells into a parallel and then adding the units serially reduces complexity in terms of voltage control for pack protection.

Building series strings first and then placing them in in parallel may be more common with NiCd packs to satisfy the chemical shuttle mechanism that balances charge at the top of charge. 2S2P is common; white papers have been issued that refer to 2P2S when a serial string is paralleled.

Safety devices in series and parallel connection

Positive temperature coefficient (PTC) switches and charge interrupt devices (CID) protect the battery from over-current and excessive pressure. While recommended for safety in a smaller 2- or 3-cell pack with serial and parallel configuration, these protection devices are often being omitted in larger multi-cell batteries, such as those for power tools.

The PTC and CID work as expected to switch off the cell on excessive current and internal cell pressure; however the shutdown occurs in cascade format. While some cells may go offline early, the load current causes excess current on the remaining cells. Such an overload condition could lead to a thermal runaway before the remaining safety devices activate.

For more information contact Michael Rogers, Uniross Batteries, +27 (0)11 466 1156,,

Supplied By: Uniross Batteries
Tel: +27 11 466 1156
Fax: +27 11 466 9109
  Share on Facebook Share via Twitter Share via LinkedIn    

Further reading:

  • Power designers are being challenged by spec changes
    21 February 2018, Supreme Electro Magnetics, Power Electronics / Power Management
    A survey conducted by Vicor has revealed that mitigating the impact of inevitable changes to power system requirements is essential to ensure projects are on time and within budget.
  • Linear LED driver
    21 February 2018, Arrow Altech Distribution (AAD), Power Electronics / Power Management
    Infineon Technologies released the BCR430U, a constant current linear LED driver IC, providing industry-leading drop performance for regulating LED current in standalone operation. No external power ...
  • Durability, dependability and other factors make for an ideal solar battery solution
    21 February 2018, Forbatt SA, Power Electronics / Power Management
    Once the sun goes down or it gets cloudy, a solar system is only as good as the method used to store the harvested solar energy. Batteries are normally used as a power bank to provide the necessary storage ...
  • PFC and offline switching ICs
    21 February 2018, RS Components (SA), Power Electronics / Power Management
    RS Components has announced availability of two new ranges of power semiconductors from Power Integrations. Delivering high energy efficiency with integrated protection features, the new offering from ...
  • 2 Watt DC-DC converters
    21 February 2018, Brabek, Power Electronics / Power Management
    The new 2 W RTC2 series modules from Recom come in a six-pin SMD open-frame package with a footprint of less than 2,13 cm². The 2:1 inputs’ voltage ranges of 4,5 to 9 V d.c. or 18 to 36 V d.c. can handle ...
  • Selecting the best inductor for a DC-DC converter
    21 February 2018, RF Design, Power Electronics / Power Management, Passive Components
    While DC-DC conversion circuitry has matured to the point that there are ‘cookbook’ design aids as well as software to help, selecting the right power inductor is a critical aspect of converter design. ...
  • Offline flyback switchers
    21 February 2018, MB Silicon Systems, Power Electronics / Power Management
    Power Integrations released its InnoSwitch3 family of offline CV/CC (constant voltage/constant current) flyback switcher ICs. The new devices achieve up to 94% efficiency across line and load conditions, ...
  • SVID and PVID enabled voltage regulator
    21 February 2018, Arrow Altech Distribution (AAD), Power Electronics / Power Management
    A new member has been added to Infineon Technologies’ IPOL (Integrated Point-of-Load) family which combines ease of use with high power density. It is the industry’s first fully integrated regulator offering ...
  • Li-ion battery management ICs
    21 February 2018, Hi-Q Electronics, Power Electronics / Power Management
    Renesas Electronics rolled out two new battery management IC solutions for lithium-ion (Li-ion) rechargeable batteries used in industrial equipment, such as electric power tools and E-bikes (bicycles ...
  • Power measuring IC for Windows 10 devices
    21 February 2018, Tempe Technologies, Power Electronics / Power Management
    Microchip announced the availability of a precision power- and energy-monitoring chip. The PAC1934 works in conjunction with a Microchip software driver that is fully compatible with the Energy Estimation ...
  • Rectifier chip diodes
    21 February 2018, Electrocomp, Power Electronics / Power Management
    Bourns announced the release of 10 new rectifier diode series for general applications, addressing the needs of portable electronics, communications, computing and video equipment manufacturers that are ...
  • Wireless power transmitter
    31 January 2018, Arrow Altech Distribution (AAD), Telecoms, Datacoms, Wireless, Power Electronics / Power Management
    The LTC4125 wireless power transmitter, made by Linear Technology, brings performance and simplicity to the transfer of up to 5 W of power wirelessly to an electrically isolated receiver capable of that ...

Technews Publishing (Pty) Ltd
1st Floor, Stabilitas House
265 Kent Ave, Randburg, 2194
South Africa
Publications by Technews
Dataweek Electronics & Communications Technology
Electronic Buyers Guide (EBG)

Hi-Tech Security Solutions
Hi-Tech Security Business Directory

Motion Control in Southern Africa
Motion Control Buyers’ Guide (MCBG)

South African Instrumentation & Control
South African Instrumentation & Control Buyers’ Guide (IBG)
Terms & conditions of use, including privacy policy
PAIA Manual


    Classic | Mobile

Copyright © Technews Publishing (Pty) Ltd. All rights reserved.