Technical guides for specifying lithium cells
Three guides cover the decisions that come before a part number: how to narrow a catalogue down to a shortlist, how 18650 and 21700 differ once they are in a pack, and what documentation a lithium consignment has to travel with.
How to choose a lithium-ion cell for a pack
A six-step selection sequence: load profile, current per cell, temperature cut-off, impedance, charge acceptance, envelope. With the arithmetic shown.
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Read the guide →18650 vs 21700: which cylindrical cell fits your pack
The two formats overlap in capacity but not in current. What changes in geometry, thermal design, tooling and cost when a pack moves between them.
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Read the guide →Lithium cell transport and safety documentation
What travels with a lithium cell shipment, which standard covers what, and how to verify that a certificate actually covers the model you are buying.
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Read the guide →Technical notes, in depth
The four parameters that decide a pack
Each of these takes one parameter from the glossary and follows it through design, measurement and failure — the parts that a definition cannot cover.
Internal resistance and DCIR: what the number predicts
ACIR and DCIR are different measurements with different uses. How each is measured, what voltage sag it predicts, and what spread a pack tolerates.
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Read the guide →Temperature and derating: why the rating has a condition attached
Why a discharge rating carries a temperature condition, how to derate when the enclosure cannot hold it, and what changes at low temperature.
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Read the guide →How to read a cycle-life claim
A cycle-life figure needs five conditions to mean anything. What "80% at 1,000 cycles" leaves out, and how to write a warranty claim you can defend.
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Read the guide →Pack design basics: series, parallel, matching and protection
Series and parallel arithmetic, what a BMS must do versus what it may do, cell matching, interconnect methods and the failure modes assembly causes.
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Read the guide →Compliance references
The standards, one page each
The transport guide gives the overview. These pages go through what each standard covers, which applications it is written for, and how to check a document actually covers the model you are buying.
How these guides are written
Four rules, applied to every page
Every figure on this site carries the condition it depends on. A discharge rating is written with the manufacturer temperature cut-off attached, because a current quoted without one is not a figure you can design against.
Every specification is labelled with where it came from. Manufacturer data sheet on file is one tier; a public catalogue page is another; a third-party listing is a third. Where no manufacturer document exists, the model stays marked pending.
No brand is ranked. The guides describe what each manufacturer builds and what documentation exists for it, not which one is better — the answer to that depends on your duty profile.
No prices, stock levels or lead times appear anywhere. Those are quoted per enquiry, and a number published on a page would be wrong before it was read.
Reading is faster than guessing
Send the duty profile rather than a part number, and the shortlist comes back with the documentation behind each candidate.