Pack Definitions & Glossary

Sometimes I don’t know where to start and hence need an A to Z to browse, hence this page on Pack Definitions & Glossary.

Ah – the ampere-hour capacity of a battery pack is the total Ah capacity of the cells in one parallel group.

Burst Disc – mechanism that can operate under extreme conditions when battery cells are venting or in thermal runaway. Thus allowing the gases to escape the pack safely.

BYD cell to body battery technology

C2B – Cell to Body is a step on from C2P and integrates some of the vehicle body parts and functions into the pack and vice versa.

C2P – 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.

Case – the enclosure for the pack.

Contactors – high power relays that are used to isolate the battery pack.

Cooling Systems – there are a number of different cooling systems / media used to extract the heat generated in a battery pack, the main options are:

  • Air cooled
  • Liquid cooled
  • Phase change
    • Active refrigerant cooling
    • Passive phase change material (PCM)
    • Two phase dielectric fluid
dielectric immersion cooling ssytem

DCIR – the DC internal resistance of a battery pack.

Fuse – passive electrical component designed to be a weak electrical link that breaks the current flow under given conditions.

HV Distribution – in high voltage (HV) battery packs the busbars join all of the collections of cells together electrically, these are fused and switched.

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

Internal Resistance – the DC internal resistance of a battery pack.

Labels – a battery pack needs a nameplate and labels that meet the requirements of the market it is to be sold for use in.

Metrics – a Pugh Matrix is a good way of making a high level comparison between applications and the key pack metrics.

In the case of mobile consumer products such as a mobile phone the lifetime of the battery is perhaps not as important as it would be in the case of a grid storage system. The mobile phone has a 2 to 3 year life before most are upgraded. A grid storage system needs 20 years of operation.

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

Pressure Equalisation Vent – when changing altitude the pressure and hence forces on a large battery pack can be significant. This can cause the vent disc to break or put pressure on the sealing system. Thus a gortex vent is often used to allow the pressure inside the pack to equalise with the ambient conditions.

Ragone Plot – graph of power density versus energy density.

Series and Parallel – the stringing of the cells in the battery pack.

SoC – the State of Charge for a battery pack is normally declared to the user based on the usable capacity window. Hence in absolute terms the SoC might be limited to a maximum of 95% at cell level, but to the user this would be shown as 100%.

SoH – State of health is the current usable capacity divided by the as new usable capacity of the pack. The user will see a lower than total capacity to increase the life of the battery.

String – a number of batteries/modules connected in series.

XEV - battery swapping

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.

Total Energy

Usable Energy

Wh/kg – gravimetric energy density of a battery pack.

Wh/litre – volumetric energy density of a battery pack.

W/kg – gravimetric power density of a battery pack.

W/litre – volumetric power density of a battery pack.