The options for the cooling systemdepend on the usage cycles, selected cell, ambient conditions and what cooling systems are available for the installation. The high level goals are: 1. minimise the temperature gradient across the cell <3°C 2. minimise the cell to cell temperature <3°C 3. do not exceed cell maximum. 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. Of course, with all of the sizing you need to consider the pack ageing, fundamentally over time the battery will: 1. decrease in capacity 2. increase in resistance That.
However, all of this takes time and hence please use this as a first approximation. The battery pack mass is roughly 1.6x the cell mass, based on benchmarking data from >160 packs. However, there are a number of estimation options and always the fallback will be to list and weigh all of the components.
The arrangement of the cells inside a battery pack is usually reported like 10s2p, for example, where 10 is the number of series cells (10s) and 2 the number of cells in parallel (2p). This means that the battery contains a total of 20 cells, as shown in the drawing above. The C-rate, in this case, is calculated from the capacity of the whole pack.
What determines the operating voltage of a battery pack?
The operating voltage of the pack is fundamentally determined by the cell chemistry and the number of cells joined in series. If there is a requirement to deliver a minimum battery pack capacity (eg Electric Vehicle) then you need to understand the variability in cell capacity and how that impacts pack configuration.
Increasing or decreasing the number of cells in parallel changes the total energy by 96 x 3.6V x 50Ah = 17,280Wh. As the pack size increases the rate at which it will be charged and discharged will increase. In order to manage and limit the maximum current the battery pack voltage will increase.
When assembling a battery pack you should use just one type of cell and balance them before assembling. Note that wiring in parallel cells which are not at the same voltage may make the cells blow up in your face. Not nice. Soldering: Cheaper and easyer for sure, but also a bit dangerous and likely to ruin your cells.
The key dimensions for these battery types are as follows: 18650 Battery: This type measures approximately 18 mm in diameter and 65 mm in height. It is commonly used in laptops and electric vehicles due to its relatively compact size.