18650 battery basics: what the numbers mean
The 18650 is the most widely used cylindrical lithium cell, and its numbers are widely misunderstood. This guide explains what each figure means and how to compare cells fairly.
Layered pack cross-section — the site's recurring diagram motif. It is a schematic, not a photograph of a product, factory or customer project, and it is not presented as a photograph of this company's factory.
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The name itself is the size: 18 mm in diameter and about 65 mm long, with the trailing zero denoting a cylindrical cell. The detail cell on this site measures 65.5 mm high and 18.4 mm in diameter, within the usual tolerance, and weighs 48 g. That standard size is the format's strength: devices, holders and packs can be designed around a known cylinder, and cells from different makers fit the same holder, even though their capacity, discharge current and cycle life differ.
Capacity, in milliamp-hours, is the headline figure and the most miscompared. A cell listed at 3000mAh, like this site's detail cell, delivers that capacity under the listing's test conditions — typically a low discharge current at room temperature. At a high discharge current, the same cell delivers less usable capacity, and at low temperature it delivers less again. Two cells compared at different discharge currents are not comparable, and a buyer should ask for the test conditions or compare cells from listings that state them on the same basis. The detail cell lists a 1.5A charging current, a 3A maximum continuous discharge current, an 800-cycle life and a self-discharge rate of 2% or less; those are that cell's figures, and other 18650 cells differ on each of them.
From cells to packs is a matter of series and parallel. Series adds voltage: 13 cells in series give about 48V. Parallel adds capacity: two strings in parallel double the amp-hours. A pack's protection board then watches the whole assembly, and the pack's rating — voltage, capacity, maximum discharge current — describes the assembly, not any single cell. A buyer who orders cells when a pack is needed, or a pack when cells are needed, has ordered the wrong product even when the chemistry matches, because the holder, wiring and protection are part of the pack and absent from the bare cell.
Bulk buying follows naturally from the format, since packs and devices consume cells by the dozen or hundred. In general industry terms, bulk inquiries are framed as quantity bands — samples, trial orders and volume orders — and the right band depends on the design's maturity. This site does not present a general quantity figure as this company's policy for any particular cell, and a bulk inquiry should still name the exact cell, because 18650 cells with the same format differ in capacity, discharge current and cycle life.
Questions to ask before you order
- What discharge current was the capacity measured at?
- Is a bare cell or a finished pack needed — and who provides protection?
- What series and parallel arrangement gives the required voltage and capacity?
- What cycle life and self-discharge does the exact cell list?
- What quantity band fits the design's maturity — sample, trial or volume?
Related pages
18650 3000mAh cell · 48V pack · 18650 range · Choosing a custom pack
How to place an inquiry, step by step
- Send the device facts. Tell us the device type, the available space (length, width and maximum thickness), the nominal voltage you need, the capacity or runtime you target, and the peak current if your device has motors, radios or heaters.
- Name the model or the chemistry. If a page on this site matches, quote its model description and listing details. If nothing matches, say so and describe the chemistry and voltage you need, so the conversation starts on the custom route.
- Confirm documents and terms in writing. Ask for the certificate set for that exact model, confirm the minimum order, the price basis and the lead time for that listing, and confirm payment and warranty terms before you pay. Terms stated for one model listing do not transfer to another model.
- Agree the sample step. Confirm whether the next step is a listed sample, an engineering sample for a custom design, or a small trial order, and what test you will run on arrival — fit in the enclosure, runtime, or peak-current behaviour.
Send all of this in one message through the contact page: device type, space, voltage, capacity, peak current, model description if you have one, and the documents you need. That is the whole inquiry — no separate form, no account, no extra step.
What to send us now
Send one message with your device type, the space the pack must fit, the voltage and capacity you need, the peak current if it matters, and the model description if a page on this site already matches. Add the documents you need — certificates are available upon request — and whether you need a listed model or a custom design. Use the contact page or write to [email protected], or call +86-755-25629920. A specific message like that is what turns a range of hundreds of models into a short, answerable question.