Battery Pack

A battery pack may have one or more cells, even thousands of battery cells. If it has multiple cells these will be connected together in series and parallel. This group of cells will need electrical busbars as interconnects, a mechanical system to hold all of the cells together, a monitoring and control system and maybe a cooling system to manage heat output from the cells.

In every aspect of the operation of the battery pack it’s capability will be limited by the weakest cell. Note that the weakest cell might change depending on the operating conditions.

Hence, careful design of the electrical, thermal and mechanical system in a pack is crucial if you want the performance to equal the sum of the parts. These are the Battery Basics.

Sizing a Battery Pack

In simple terms this will be based on the energy and power demands of the application. An overview and a few case studies would be helpful.

usable SoC for different applications

The application of the battery pack is quite fundamental to sizing it and setting the usable SoC window.

High power packs need to operate over a narrower state of charge window if the power delivery is to be consistent.

A long range BEV will have a very ‘wide’ usable SoC of around 90 to 95%. A HEV that discharges and charges the pack in an aggressive way would need a ‘narrow’ usable SoC of around 30%.

Thermal Sizing

There may also be a requirement to size a battery pack to have a passive thermal system, as such the heat capacity of the pack would need to be sized to suit the typical usage cycle.

The thermal and electrical performance of the pack are the first things to look at when sizing a battery pack.

XEV - battery swapping

Designing Swappable Batteries

Unlike fixed batteries that can be redesigned with each new generation of vehicles, swappable batteries inherit outer design, power output and data exchange protocols of their precursors for maximum utilization purposes. It’s typical of swap operators to mix modern batteries into their stocks of older ones and offer them at different prices.


A great way to look for ideas, options and check the specifications is to look at competitor battery packs. Our section on Benchmarking is growing all the time.

Sodium Ion Battery Pack

This low cot battery technology is approaching fast with lots of announcements.

Achieving 120Wh/kg at pack level.

The modular vs dedicated BEV platform is an interesting problem facing automotive OEM’s as they balance their need to produce Internal Combustion Engine (ICE) vehicles and Battery Electric Vehicles (BEV). The trouble is we are in a world that still wants both vehicle options and vehicle platforms are expensive.

battery pack generations

Pack Generations

When we look at automotive battery pack design there have been a number of pack generations. The general theme is to simplify and hence reduce the cost.

Parts List for a Battery Pack just lists the major systems and the parts, including software for the BMS.

Mercedes Benz EQS battery

Cell to Pack

Cell to Pack is all about reducing cost and increasing the volumetric density of battery packs. This is primarily aimed at road vehicle battery design. This can offer some significant increases in energy density and cost reductions. However, this does remove barriers between cells and hence brings into focus the task of how to stop cell to cell propagation.

BYD cell to body battery technology

Cell to Body

The next step is to place the cells directly into the vehicle body structure: Cell to Body or CTB or C2B. At first you might think that this is just the next obvious step, however, there are a number of questions around manufacturing, repair and service that we need to understand.

Electrode to Pack

Is this the ultimate design for energy density?

This removes the cell and module packaging elements.

Joining Techniques for Pack Enclosures

  1. Mechanical / Adhesives
  2. Friction Stir Welding
  3. GMAW Welding
  4. Hybrid Laser Welding
  5. Hot Wire Laser
  6. Precision Power Laser

Assessing a Pack Supplier

If you’re assessing a pack supplier what do you need to think about? What questions should you ask? Ensure you have a clear set of requirements beforehand, at a high level these need to be:

  • usable energy
  • peak power
  • continuous power
  • voltage range
  • charge time
  • dimensions
  • maximum weight
structure of a battery pack

Stuck and need a different view of pages? Check out Pack Definitions and Glossary.