## Cell Resistance Metric

When looking for the best performing battery pack the internal resistance of the cell plays a significant role. Simple Ohm’s Law shows that as we deliver a voltage we get a voltage drop equal to the current times the resistance. The heat generation in a cell is a summation of Joule and Entropic heating. At … Read more

## Data Required to Size a Pack

When thinking about sizing a battery pack it is worth stopping and considering the data required to size a pack. These are the requirements. If you don’t have these then the design is likely to change considerably, these changes will cost time and can ultimately end in a poorly optimised design. The usable energy for … Read more

## 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: We could just look at Cell to Pack Mass Ratio as this is a metric used to establish how efficient a particular … Read more

## Maximising Pack Energy Density

How can we go about maximising pack energy density? What can we look at to reduce the mass and volume? Where are the opportunities given a defined cell? A great example of shrinking the size of a battery pack is the Mercedes Vision EQXX research car. The advantage they had was a much more energy … Read more

## Battery versus System Voltage

When we look at the battery versus system voltage we have to remember that these are working together. In fact we have to look at the complete system and all components to ensure they can work together over the maximum and minimum voltage range. This will normally be the maximum charge voltage and the minimum … Read more

## Higher Voltage Packs

Why are we moving to higher voltage packs? We know that the battery cell is not a perfect current source as it also has an internal resistance. Symbolically we can show a cell with the internal resistance as a resistor in series. Rint is the DC internal resistance, sometimes abbreviated as DCIR. The DCIR is not … Read more

## Battery Pack Volume

Often it is difficult to estimate the battery pack volume, hence here is an approximation based on data fitting. Hence a first approximation is that the battery pack volume will be 5x the total energy in kWh. A 100kWh battery would have a volume of 500 litres. If this was a design optimised for volume … Read more

## Pack Mass from Cell Density

It is possible to use the battery pack database to estimate the pack mass from cell density. The key relationship we have is between cell and pack gravimetric energy density. This graph has been pulled together by scouring the internet for cell and battery data. The ratio of cell density to pack density is 0.6235 … Read more

## Cold Climate EV Range

Cold climate EV range is determined by a number of factors. First of all though, let’s look at the range results as conducted by Motor.no in their winter range tests. An impressive test with 29 different electric vehicles. Read the full description of the tests on the Motor page and there you can see some … Read more

## Cell Capacity and Pack Size

Obviously Cell Capacity and Pack Size are linked. The total energy content in a battery pack in it’s simplest terms is: Energy (Wh) = S x P x Ah x Vnom  Hence the simple diagram showing cells connected together in series and parallel. What about flexibility in pack size? There are very good reasons for … Read more