Choose a lithium battery by starting with the application, not the largest Ah figure or the most familiar brand. Establish the voltage window, usable-energy target, load profile, mechanical envelope, environment and required service life. Then compare specific cells or finished packs against those constraints, and qualify the remaining candidates with matched documents and samples.
This approach works whether a buyer already has a preferred manufacturer or is comparing several Chinese battery brands. It also prevents a common mistake: selecting a cell first and discovering later that the charger, enclosure or operating duty requires a different solution.
Step 1: decide what you are actually buying
A cell, a module and a finished pack are different purchasing scopes. Cells provide the electrochemical building blocks. A pack adds an electrical architecture and may include monitoring, protection, balancing, interfaces, mechanical support and thermal provisions. The presence of a BMS is not a complete description of these functions. S09
If a technical team already controls pack design and assembly, the enquiry can focus on cells and their integration requirements. If the project needs a battery that connects to equipment through defined power and communication interfaces, request that finished scope explicitly.
State what is included: enclosure, connector, cable, charger, communication protocol, firmware behavior, mounting and any application-specific tests. Otherwise, a cell-only price may appear attractive simply because necessary work sits outside the quote.
CELL & PACK's featured catalogue is one starting point. A sourcing request can also specify another brand or model, or describe the required product without a selected model. Manufacturer or customer engineering teams remain responsible for technical design and suitability assessment.
Step 2: separate hard constraints from preferences
Hard constraints eliminate candidates. Preferences rank the candidates that remain. A product that cannot stay within the equipment's electrical limits does not become suitable because it is cheaper or lighter.
Scroll horizontally to read every column.
| Hard constraint examples | Preference examples |
|---|---|
| Required operating voltage range | Lower mass within an acceptable range |
| Load duration and minimum loaded voltage | Higher energy margin |
| Maximum available installation space | Preferred brand or terminal style |
| Environmental and protection requirements | Lower integration effort |
| Required product evidence and permitted use | Lower commercial cost |
Some requirements can move between the columns as a project develops. A connector may be negotiable during early design but fixed for a replacement project. Record that distinction rather than treating every desired feature as mandatory.
Also distinguish a known requirement from a guess. A measured load trace is different from “probably 500 W.” Early assumptions are useful, but they need a planned point of confirmation.
Step 3: define the complete voltage window
Record the equipment's highest and lowest acceptable operating voltage, startup behavior and charging interface. Ask whether those limits apply at the battery terminals or after a converter. Include load-related voltage drop and the intended operational reserve.
Nominal pack voltage is only a description. For identical cells, series arithmetic gives:
V_nominal,pack = Ns × V_nominal,cell
The corresponding upper and lower limits depend on the actual cell and pack settings. A candidate can have a suitable nominal voltage yet exceed the equipment limit when fully charged. Voltage limits are explicitly separated in battery characterization methods for this reason. S02
Hypothetical screen: equipment accepts no more than 54 V at its battery input. A proposed 16-series candidate with an assumed 3.65 V upper cell limit gives 58.4 V. That candidate fails this screen regardless of its Ah, price or advertised life. The example illustrates a requirement check; it does not specify a real product or a charging recommendation.
At the lower end, use voltage under the required load, not only resting voltage. A cell reaching the lowest allowed voltage earlier can determine usable energy before nominal capacity is exhausted.
Step 4: calculate the load's energy requirement
Energy is the sum of power over time. For a simple profile, divide the operating period into segments and add their energy. Include electronics and accessories at the correct boundary rather than adding an unexplained universal safety factor.
Consider a hypothetical mobile equipment project with 180 W average drive demand and 20 W of auxiliary load for two hours, both measured after the power converter:
E_load = (180 + 20) W × 2 h = 400 Wh
Now assume, solely for preliminary arithmetic, 90% conversion efficiency, an operating window using 80% of reference energy, and an end-of-service energy-retention factor of 80%:
E_reference ≈ 400 / (0.90 × 0.80 × 0.80) = 694 Wh
This is a first-pass reference requirement, not a promise of runtime or a prescription for reserve factors. These factors are separate assumptions: efficiency, selected operating window and aging. Do not multiply them again if the supplied usable-energy test already includes the same effects. Temperature and load-dependent performance still need relevant evidence.
For a variable mission, use the actual time sequence. A machine may have a high peak but low average energy demand, while another with modest power may need much more energy because it runs continuously. The energy guide explains the distinction between Ah, nominal Wh and delivered energy.
Step 5: specify power, current and repeated peaks
Provide continuous and peak demand with duration, repetition, recovery and minimum voltage. “Maximum 600 W” is incomplete if no one knows whether it lasts one second or the entire shift.
For the same illustrative project, a 600 W demand after a 90%-efficient converter would draw approximately:
I_pack ≈ 600 / (36 × 0.90) = 18.5 A
at 36 V. The current would be lower at a higher operating voltage, assuming the same power and efficiency. In practice, efficiency can vary, and the relevant low-voltage condition must be established by the system team.
Cell current also depends on parallel arrangement and current sharing. A theoretical split among parallel cells is a starting point, not proof that every cell experiences exactly the same current. Confirm the pack limits for connections, protection and temperature as well as the cell rating. S09
Charge demand is a separate profile. State the required turnaround time, temperature and available charger power. A discharge-capable cell is not automatically capable of the same charging current. S30
Step 6: screen chemistry and format using the project priorities
LFP and NMC are both lithium-ion chemistry families. A chemistry choice informs the search, but exact performance still belongs to a product. LFP is commonly investigated for durability, thermal stability and economics; energy-oriented NMC is commonly investigated for demanding energy-per-mass or energy-per-volume targets. S05 S06
Next consider cylindrical, prismatic and pouch construction. Their integration requirements differ; the shape does not independently establish chemistry or safety. Mechanical envelope, terminal arrangement, support, connections and cooling can change the attractiveness of a candidate. S07
Use these categories to organize a shortlist rather than make the final decision. Read LFP vs NMC and cell format comparisons when the project can still accommodate several approaches.
For an existing product replacement, do not assume flexibility that does not exist. Fixed charger behavior, firmware and mechanical interfaces may sharply restrict the shortlist.
Step 7: budget pack mass and space, not just cell mass and volume
A useful mass budget separates cells, busbars and wiring, BMS and protection, enclosure and restraint, connectors, and thermal hardware. A volume budget needs actual geometry and clearance—not only a total in liters.
Consider two imaginary packs containing the same nominal energy. One uses lighter cells but more supporting structure; the other uses heavier cells but a different integration approach. A cell-level Wh/kg ranking alone cannot resolve the complete result. System design models therefore treat energy, power, structure and cost together. S08
Ask for both the proposed assembly drawing and a clear scope of included hardware. If a quoted mass is cells-only, label it accordingly. If the final enclosure is not defined, treat the finished mass as an estimate rather than a confirmed specification.
Step 8: describe environment and end-of-service requirements
Separate charging, operation and storage environments. A machine charging indoors and operating outdoors has a different thermal history from one charging immediately after a cold shift. Cold charging needs product-specific controls; permission to discharge at a temperature is not permission to charge there. S15
Define required remaining energy and power at the end of service. For standby equipment, readiness and calendar exposure may matter more than high advertised cycle counts. For repeated daily operation, duty and throughput become central. Battery lifetime tools incorporate temperature, SOC history, current, cycle depth and pack balance because these interact. S12
Other environmental requirements may include vibration, ingress exposure, altitude or installation orientation. State the actual requirement and applicable test basis. Do not add certification names indiscriminately; the intended application and destination determine which evidence is relevant.
Step 9: compare evidence and commercial scope together
A technically attractive candidate is not yet an executable purchase. Confirm the offered model, product state, applicable specification, sample availability, document-sharing scope, quantity conditions and delivery basis.
Scroll horizontally to read every column.
| Procurement question | Evidence or clarification to request |
|---|---|
| Is the quote for the intended product? | Full model and agreed version, not only a similar name |
| Can the proposed samples be evaluated meaningfully? | Sample identity and an agreed evaluation plan |
| Will later supply match the evaluated item? | Product/version controls and change communication |
| Do the documents cover the actual object? | Matched specification, transport evidence and application evidence as relevant |
| Are quotes comparable? | Same product scope, quantity, currency and delivery basis |
| What is still open? | An explicit list with a responsible party and next decision point |
Transport evidence and application-performance evidence answer different questions. A UN 38.3 test summary is not a runtime or cycle-life guarantee. S17 For a deeper document workflow, use the safety and documentation guide.
Step 10: qualify a shortlist rather than testing everything
The point of the earlier screens is to reduce the number of costly evaluations. Start with the candidates that satisfy hard requirements and have enough supporting information to evaluate.
An agreed sample program can address capacity/energy at relevant conditions, load and voltage response, charging, interfaces, mechanical fit and application behavior. Qualified personnel should select safe methods and limits. Transport-type or destructive abuse testing is not an improvised acceptance check for an ordinary purchasing team.
Record the outcome against requirements. A useful result is “meets energy requirement at the specified duty; communication behavior still unresolved,” not simply “sample looks good.” Differentiate measured sample results, manufacturer declarations and assumptions so that the batch order does not inherit unsupported conclusions.
A one-page sourcing brief
A strong first enquiry can be concise:
Scroll horizontally to read every column.
| Field | Information to provide |
|---|---|
| Purchase scope | Cells, module or finished pack; design responsibilities |
| Preferred product | Brand/model if known, or open to candidates |
| Voltage | Equipment range and charging arrangement |
| Energy | Required operating time and load profile |
| Power | Continuous and peak demand, duration and repetition |
| Mechanical | Installation envelope, mass limit and interfaces |
| Environment/life | Charging, operating and storage conditions; end-of-service need |
| Commercial | Sample/batch quantities, destination and target timing |
| Evidence | Documents and acceptance conditions already required |
Leave unknown fields open rather than inventing precision. The purpose is to direct the next discussion efficiently.
Common questions
Should I start with a brand or a specification?
Either can be useful. A specified brand/model simplifies identification; a clear requirement allows candidate comparison. Neither removes the need to confirm the offered product and operating conditions.
Is the largest Ah the best starting point?
No. Voltage, power, mechanical limits and usable energy can eliminate a high-Ah candidate. Compare energy at the relevant voltage and load.
Should I specify a fixed chemistry before asking for a quote?
Only when the project already requires it. Otherwise, state the constraints and preferences separately so alternatives can be evaluated fairly.
Can the online calculator replace qualification?
No. It supports nominal electrical and mass arithmetic. It does not validate protection, heat, compatibility or safe operating limits.
Move from requirements to candidates
CELL & PACK provides multi-brand cell sourcing and finished-pack procurement coordination. Our online catalogue showcases featured products; it is not the boundary of the sourcing service. Send a brand, model or application-based enquiry and use the datasheet guide to review the candidates that follow.
Sources and further reading
- S09 Texas Instruments. BQ76952 battery monitor and protector.
- S02 Idaho National Laboratory / U.S. DOE. Battery Test Manual for Electric Vehicles, Revision 3 (June 2015), INL/EXT-15-34184.
- S30 Texas Instruments. BQ25170 800-mA linear battery charger for 1-cell Li-ion and LiFePO4.
- S05 LG Energy Solution. LFP Battery — Materials.
- S06 LG Energy Solution. NCM Battery — Materials.
- S07 TRUMPF. Battery cells and modules.
- S08 Argonne National Laboratory. Modeling the Performance and Cost of Lithium-Ion Batteries for Electric-Drive Vehicles, Third Edition.
- S15 National Laboratory of the Rockies / Journal of The Electrochemical Society. Investigation of Lithium Plating-Stripping Process in Li-Ion Batteries at Low Temperature Using an Electrochemical Model.
- S12 National Laboratory of the Rockies. BLAST: Battery Lifetime Analysis and Simulation Tool Suite.
- S17 U.S. PHMSA. Interpretation 22-0007 (20 October 2022).