If you’ve spent your career in mechanical engineering, power electronics, software, automotive systems, or aerospace — and you’re now working on batteries — you’re in the right place.
BatteryDesign.net is written by engineers, for engineers. The assumption here is that you can read a datasheet, you understand thermal gradients and control loops, and you don’t need the basics of Ohm’s law explained. What you might need is a fast, reliable orientation to a field that has its own vocabulary, its own failure modes, and its own set of design trade-offs that take time to internalise.
This page is that orientation.
Start with the Mental Model
A battery system has a clear hierarchy. Understanding where each layer sits — and how each layer constrains the ones above it — is the foundation everything else builds on.
Every design decision propagates both up and down this stack. The choice of cathode chemistry sets the voltage window, which constrains the BMS thresholds, which constrains the contactor ratings, which affects the pack enclosure design. A thermal runaway event in a single cell can destroy a pack worth tens of thousands of pounds if the propagation path isn’t designed out. The interdependencies are deep and non-obvious — and that’s what makes battery engineering genuinely interesting.
The site is structured to follow this hierarchy.
The Stack, Layer by Layer
1. Chemistry
What the cell is made of, and why it matters to the engineer.
Cell chemistry determines energy density, power capability, thermal stability, cycle life, cost, and safety behaviour. These are not independent variables — every cathode formulation involves trade-offs, and understanding those trade-offs is the first thing a battery engineer needs to internalise.
The dominant chemistries in current production are:
| Chemistry | Abbrev. | Key strength | Key weakness |
|---|---|---|---|
| Lithium Iron Phosphate | LFP | Safety, cycle life, cost | Lower energy density |
| Lithium Nickel Manganese Cobalt | NMC | Energy density, versatility | Cost, thermal stability at high Ni |
| Nickel Cobalt Aluminium | NCA | High energy density | Thermal sensitivity, cost |
| Nickel Cobalt Manganese Aluminium | NCMA | Best-in-class high-Ni stability | Manufacturing complexity |
| Sodium Ion | Na-Ion | Cobalt-free, low cost | Lower energy density than Li-ion |
| Solid State | SSB | Safety, energy density (future) | Not yet at volume production |
→ Chemistry overview → Chemistry roadmap → Lithium ion chemistry → LFP → Sodium-ion → Solid state
2. The Cell
The fundamental unit. Everything else is built around its constraints.
Cells come in three main formats: cylindrical, prismatic, and pouch — plus the blade cell as a prismatic variant optimised for cell-to-pack designs. Each format has different mechanical integration requirements, cooling characteristics, and assembly implications for the pack engineer.
Key cell parameters to understand early:
- Nominal voltage and operating window — the voltage range the BMS must manage
- Capacity (Ah) and energy (Wh) — how much charge and energy the cell stores
- C-rate — charge/discharge rate relative to capacity; 1C discharges the cell in 1 hour
- DCIR — DC internal resistance; drives voltage drop under load and I²R heating
- Gravimetric energy density (Wh/kg) and volumetric energy density (Wh/L) — the key metrics for comparing cells
- Cycle life — how many charge/discharge cycles before capacity falls to 80% of original
The cell benchmarking database is one of the most used resources on the site — real measured data from real cells, not marketing specifications.
→ Cell overview → Cell formats → Cell design → Key cell metrics → Cell benchmarking database → Cell manufacturers A–Z
3. Module Design
The intermediate assembly — grouping cells before pack integration.
Modules are groups of cells with their own mechanical structure, electrical interconnects, voltage sensing harness, and temperature sensors. Not every pack uses discrete modules — cell-to-pack (C2P) architectures skip the module entirely, and cell-to-body (C2B) goes further by integrating the cells into the vehicle structure — but understanding module design is still essential because most packs in the field use them.
→ Module design → Module manufacturers → Module benchmarking
4. The Battery Pack
Where all the constraints come together.
Pack design integrates the mechanical, electrical, thermal, and safety requirements into a single enclosure. The pack engineer is managing competing demands simultaneously: minimise mass and volume, maximise structural integrity, maintain cell temperatures within ±2°C, route high-voltage busbars with adequate creepage and clearance, and ensure the whole assembly survives a decade of vibration, thermal cycling, and abuse events.
This post has been built based on the support of and sponsorship from: illumion, Custom Power, Quarto Technical Services, Eatron Technologies and About:Energy
Key topics for engineers new to pack design:
Sizing. Pack energy and power are determined by the series/parallel cell configuration (S×P) and cell specification. The pack sizing page walks through the methodology from application requirements to S×P selection.
Enclosure. The pack enclosure manages IP rating (typically IP67 or IP6K9K), structural load paths, sealing against ingress, pressure equalisation, and in some designs crashworthiness as a structural member.
Thermal management. The most consequential thermal design decision is the cooling architecture — air, liquid (water-glycol cooling plate), immersion dielectric, or refrigerant. Cooling plate design is the most common approach in automotive; the design trade-offs between inlet/outlet geometry, flow velocity, and temperature uniformity across the pack are covered in depth.
High voltage architecture. Pack voltage ranges from 48V (mild hybrids) through 400V (most current EVs) to 800V+ (Porsche, Hyundai, newer platforms). Higher voltage reduces current for a given power, reducing conductor cross-sections and I²R losses — at the cost of more cells in series and more demanding isolation requirements.
→ Pack design → Pack sizing → Pack enclosure → Key pack metrics → Pack benchmarking → 400V vs 800V architecture
5. Battery Management System (BMS)
The brain of the pack. More demanding than most embedded systems engineers expect.
The BMS is the hardware and software control system that measures every cell voltage and temperature, estimates state of charge (SoC) and state of health (SoH), controls the contactors, manages cell balancing, protects against overcharge and overdischarge, and communicates pack status to the vehicle or system controller.
For engineers coming from embedded systems or automotive electronics, the BMS architecture will be familiar in structure — but the algorithms and the consequences of errors are not. A SoC estimation error of 5% in either direction has direct consequences for range, safety, and cell lifetime. A missed isolation fault can be fatal. The functional safety requirements (ISO 26262, typically ASIL C or D for main BMS functions) are demanding.
Key BMS topics to understand:
- SoC estimation — coulomb counting, OCV-based, and Kalman filter approaches
- SoH estimation — capacity fade and resistance growth tracking over lifetime
- Cell balancing — passive (dissipative) vs active (redistributive), and when each is appropriate
- Contactor control and pre-charge — why the pre-charge circuit exists and what happens without it
- Isolation monitoring — detecting insulation breakdown in the HV circuit before it becomes a safety event
- Functional safety — ISO 26262 ASIL levels, hardware and software safety requirements
→ BMS overview → BMS algorithms → BMS hardware → Sensors → Harness design → Cloud data and fleet analytics
6. High Voltage System
The electrical architecture between the pack and the load.
The high voltage system encompasses the contactors, fuses, Battery Disconnect Unit (BDU), busbars, connectors, current sensors, and the High Voltage Interlock Loop (HVIL). These are not exotic components — but their sizing, the creepage and clearance requirements at 400–800V, and their interaction with the BMS logic require careful attention.
A pre-charge resistor sized incorrectly will either fail to limit inrush current adequately or add unnecessary resistance to normal operation. A busbar sized only at 5A/mm² without electrothermal analysis may overheat at pulse loads. These are the details that catch engineers new to HV design.
→ High voltage system → Battery Disconnect Unit → Busbars → Contactors → Fuses → HVIL → Current sensors
7. System Integration
How the pack fits into the wider application.
BatteryDesign.net covers battery applications across EVs (BEV, HEV, PHEV, FCEV), battery energy storage systems (BESS), industrial vehicles, maritime, aerospace, and consumer products. The system context matters because it defines the duty cycle, the thermal environment, the lifetime requirement, and the regulatory framework the design must satisfy.
→ System overview → Battery Energy Storage Systems (BESS) → Electrification architectures → Power electronics
Five Pages Worth Reading First
If you read nothing else in the first week, read these. They build the core mental models that everything else references.
1. Battery Basics The fundamental electrical and thermal behaviour of a cell — OCV, DCIR, capacity, C-rate, and how they relate. The vocabulary everything else uses.
2. Series and Parallel How cells are strung together to achieve target voltage and capacity. Simple in principle, consequential in practice — the weakest cell sets the limit for the whole pack.
3. Thermal Runaway The failure mode that makes battery engineering different from most other electrical engineering. Understanding what triggers it, how it propagates, and how pack design mitigates it is non-negotiable.
4. State of Charge Estimation SoC is the battery’s equivalent of a fuel gauge — except it cannot be measured directly and must be estimated from voltage, current, temperature, and model. The approaches, their limitations, and their accuracy trade-offs are covered in the BMS algorithms section.
5. Pack Benchmarking Real data from teardowns of production packs — Tesla, BYD, BMW, CATL, Porsche, Rivian and many others. The fastest way to calibrate your intuition for what good pack design looks like in practice.
The Reference Resources
These are the tools you’ll return to repeatedly, not just once.
Cell Benchmarking Database Measured performance data across hundreds of production cells. Filter by chemistry, format, manufacturer, energy density.
Pack Benchmarking Database Architecture and performance data from real EV and BESS packs. Cell-to-pack ratios, gravimetric and volumetric energy density, cell format and chemistry.
The Battery A to Z — browse online A searchable glossary of terms, definitions, and explanations covering over 400 entries from 12V Battery through to Z Stack. If a term appears on the site and you’re not sure what it means, it’s in here.
The Battery A to Z — free PDF download Version 1.38, 70+ pages. Download it, keep it open alongside whatever you’re working on.
Downloadable Products Spreadsheets, databases, and calculators — including the Cell Database and Pack Database in downloadable format.
Battery Calculators Pack sizing, series/parallel configuration, energy and power calculations, cell-to-pack ratios.
Things That Surprise Engineers New to Batteries
A few non-obvious things that come up consistently:
The voltage window is tighter than you expect. Most lithium cells have a total voltage range of about 1.5–2V, and the usable window the BMS permits is often narrower still. Exceeding the upper voltage limit by even a few hundred millivolts accelerates ageing significantly. Dropping below the lower limit risks copper dissolution and dendrite formation. The BMS is not just a safety device — it is actively managing lifetime.
Temperature uniformity matters as much as absolute temperature. A ±5°C gradient across cells in a series string means those cells age at different rates. Over thousands of cycles, this divergence accumulates until cell imbalance becomes a capacity-limiting constraint. Thermal management design for uniformity is as important as thermal management for absolute maximum temperature.
First-cycle irreversible capacity loss is real and unavoidable. During the first charge, the anode SEI (solid electrolyte interphase) forms and consumes lithium that is never recovered. This is not a defect — it is a fundamental feature of lithium-ion electrochemistry. It is why formation cycling is a manufacturing step, and why initial coulombic efficiency appears in cell datasheets.
The cell datasheet capacity is measured at a specific C-rate and temperature. At 2C discharge and −10°C, the available capacity may be 70% of the datasheet figure. At the same rate and +45°C, it may be 95%. Real application duty cycles require characterising the cell across the full operating envelope, not just at the nominal condition.
BMS functional safety is more demanding than most automotive ECU development. ISO 26262 at ASIL C or D requires systematic hazard analysis, safety goals, safety requirements, design verification, and documented evidence of compliance. If you’re coming from body electronics or infotainment development, the rigor is substantially higher.
Pack cost is dominated by cells. Cells typically represent 60–75% of total pack cost. This means that cell selection — chemistry, format, manufacturer, and purchasing volume — has more leverage on pack economics than any other design decision. Understanding the cell market, the contract structures, and the relationship between volume and price is a commercial skill that battery engineers in OEM or tier-1 roles need to develop alongside the technical work.
Stay Current
The field moves fast. New cell chemistries are commercialised, benchmark data from new vehicles emerges, and the regulatory landscape (particularly EU Battery Regulation and battery passport requirements) is evolving continuously.
The newsletter covers new posts, new benchmarking data, and notable developments roughly every two weeks. It’s free and there’s no marketing spin — the same tone as the site.
→ Sign up to the newsletter → Latest articles
If you have a topic you’d like to see covered, or you’d like to contribute an article from your own area of expertise, reach out directly: nigel@batterydesign.net
BatteryDesign.net — from chemistry to pack