Everything Other than Cells

The cells in a battery pack weigh a lot, but everything other than cells also weighs a good percentage of the total.

For a 100kWh battery pack there is 175kg to 275kg of:

  • structure
  • cooling
  • busbars
  • enclosure
  • BMS
  • BDU
  • fire protection
  • sensors

We could just look at Cell to Pack Mass Ratio as this is a metric used to establish how efficient a particular design is.

cell to pack mass ratio
Cell to Pack Mass Ratio

An interesting benchmark, but there are some things to note as general guidance:

  • Larger battery packs will have a better ratio as some of the overheads are fixed (eg contactors, fuses)
  • Passively cooled packs should have a better mass ratio, however, the Nissan Leaf proves this wrong.
  • Packs should include coolant mass as part of the total, however, this is often missed.
  • Cell to Pack designs should have a higher mass ratio
  • Structural packs will have a lower mass ratio

The trouble is here we have plotted everything and that picture will change depending on the cell format, the charge/discharge rate and the level of integration into the system structure.

2013 BMW i3 battery pack

One of the most interesting designs is the original BMW i3:

  • Cells = 197kg
  • Pack = 235kg
  • Cell to Pack Mass Ratio = 84%

The battery enclosure weighed just 24kg

This post has been built based on the support and sponsorship from: Eatron TechnologiesAbout:EnergyAVANT Future MobilityQuarto Technical ServicesTAE Power Solutions and The Limiting Factor. 

Pack Mass Estimation

Battery pack mass estimation is a key parameter required early in the conceptual design. There are a number of key reasons for estimating the mass, one of the main ones being the significant percentage it is of the overall mass of the complete system.

This calculator uses benchmark data to estimate the mass of everything other than the cells.

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