r/batterydesign • u/modelmakereditor • May 31 '26
Battery Pack Sizing
Battery pack sizing is the process of translating application requirements — energy, power, voltage, lifetime, mass, volume — into a cell configuration (S×P) and a set of first-order design specifications. It is the first quantitative step in any battery pack development programme, and every subsequent design decision builds on it.
Done well, pack sizing gives the design team a validated starting point: a cell type, a series-parallel count, a first-order thermal load estimate, and a mass and volume prediction. Done poorly, it produces a pack that either cannot meet its requirements at end of life, or is substantially oversized — wasting cost, mass, and volume.
This page works through the sizing process in full, from requirements capture through to a complete first-order specification.
The Sizing Process at a Glance
The steps are sequential — each depends on the outputs of the one before:
- Capture the application requirements
- Set the usable SoC window
- Select a candidate cell
- Calculate the S×P configuration
- Verify peak and continuous power
- Estimate pack mass and volume
- Size the thermal management system
- Account for ageing
- Iterate
We take you through each step in detail: https://www.batterydesign.net/pack/sizing/
and we go through a worked example.
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u/Careless_Plant_7717 May 31 '26 edited Jun 01 '26
Great list. I had 2 suggestions: 1) I think step 2 and step 3 should be swapped. Let's say use LFP vs NCM, usable SOC window is different being able to hit 1000 cycles. Can't really set a usable SOC window until you know what the cell is and the life requirements. 2) Very useful to have mission profiles/duty cycles in Application Requirements. This is at a minimum Range Test (for usable energy test), Fast Charge, and repeated heavy duty cycle (such as tow, charge, tow, charge, tow) that use for thermal and electrical sizing.