What's the difference between 18650 and 21700 besides size?

The 21700 is 3 mm wider and 5 mm longer. Its ~47% greater volume holds more active material: typical capacity 4000-5000 mAh versus 2500-3600 mAh for the 18650. Discharge rates are also higher (Molicel P42A — 45A CDR). Modern power tools (Makita 40V, Milwaukee M18) are transitioning to 21700.

Can I replace 18650 with 21700?

No — they're physically different sizes and not interchangeable. A 21700 won't fit in an 18650 bay without modification. However, if you're repacking a battery pack, we at SATER can recalculate the configuration and use 21700 cells if the housing design allows it, giving you greater capacity from the same number of cells.

Is it true that 18650 capacity doesn't exceed 3600 mAh?

As of 2026, yes. The maximum real capacity of an 18650 cell from a Tier 1 manufacturer is around 3600 mAh. Any cell marked "4000 mAh" or above is a counterfeit.

How can I find out which cells are in my battery pack?

Open the housing (carefully — don't short the contacts) and read the markings on the cells. Original manufacturers apply laser markings with model number and production date. If there are no markings, unbranded cells were likely used. Bring the battery to us — we'll identify the cell type and offer a quality replacement.

Where in Riga can I get a battery repacked with quality cells?

At the SATER service centre, Silmaču iela 6, we repack battery packs for power tools, robot vacuums, and other equipment. We use only tested cells from Sony/Murata, Molicel, Samsung SDI, LG, and Panasonic. Every cell is tested before installation. We've been operating since 1993 — over 30 years of experience.

The Complete Guide to 18650 and 21700 Battery Cells — Chemistry, Brands, Capacity

Lithium cylindrical cells in the 18650 and 21700 formats are the building blocks of virtually all modern rechargeable battery packs: from laptops and power tools to robot vacuums. At the SATER service centre, we work with these cells daily — repacking power tool battery packs, replacing cells in robot vacuum batteries, and assembling custom battery packs to order.

This article is a detailed guide for anyone wanting to understand the subject: from physical dimensions to spotting counterfeits.

What the Numbers Mean: 18650 and 21700

The format name is its dimensions in millimetres:

18650 = 18 mm diameter × 65 mm length (the 0 denotes cylindrical form)
21700 = 21 mm diameter × 70 mm length

The 18650 format appeared in the early 1990s and became the de facto standard. Sony was the first to mass-produce 18650 cells for laptops. The 21700 format is newer, developed by Tesla with Panasonic for electric vehicles (Model 3, 2017). Thanks to its greater volume, the 21700 holds 35-50% more energy.

Format Comparison

Swipe to see the full table

Parameter	18650	21700
Diameter	18 mm	21 mm
Length	65 mm	70 mm
Volume	~16.5 cm³	~24.2 cm³
Typical capacity	2000-3600 mAh	3000-5000 mAh
Weight	44-50 g	60-72 g
Applications	Laptops, tools, robots	Tools, EVs, power banks

Chemistry Types

Not all lithium cells are alike. The cathode's chemical composition determines key characteristics: capacity, discharge rate, safety, and lifespan.

INR — Nickel-Manganese-Cobalt (NMC)

The most common type in modern cells. A balance between capacity, current delivery, and safety.

Typical 18650 capacity: 2500-3600 mAh
Discharge rate: medium-high (10-35A)
Examples: Samsung 25R (2500 mAh, 20A), Samsung 30Q (3000 mAh, 15A), LG HG2 (3000 mAh, 20A)

ICR — Cobalt (LCO)

High capacity but low discharge rate and elevated thermal runaway risk. Requires a protection PCB.

Typical 18650 capacity: 2600-3400 mAh
Discharge rate: low (2-5A)
Examples: Panasonic NCR18650B (3400 mAh, 4.87A)

IMR — Manganese (LMO)

High discharge rate and safety at the cost of lower capacity.

Typical 18650 capacity: 1500-2100 mAh
Discharge rate: high (20-30A)

IFR — Iron Phosphate (LFP)

Maximum safety and longevity (2000-5000 cycles), but lower voltage (3.2V instead of 3.6-3.7V) and less capacity.

Nominal voltage: 3.2V (not interchangeable with INR/ICR!)

Important: IFR/LFP cells CANNOT replace INR/ICR without reconfiguring the BMS — the voltage differs.

Capacity vs Discharge Rate

CDR vs Pulse Current

CDR (Continuous Discharge Rating) — the maximum current a cell can deliver continuously without overheating. The most important parameter for power tools.
Pulse current — short-term (typically 1-10 seconds) maximum current. Many manufacturers advertise this figure, which can be misleading.

Swipe to see the full table

Cell	Capacity	CDR	Energy	Application
Samsung 40T (21700)	4000 mAh	35A	14.4 Wh	High-power tools
Molicel P42A (21700)	4200 mAh	45A	15.1 Wh	High-power tools
Samsung 50E (21700)	5000 mAh	9.8A	18.2 Wh	High-capacity packs
Sony VTC5A (18650)	2500 mAh	25A	9.0 Wh	High-drain
Sony VTC6 (18650)	3000 mAh	15A	10.8 Wh	All-rounder
Samsung 30Q (18650)	3000 mAh	15A	10.8 Wh	All-rounder
LG MJ1 (18650)	3500 mAh	10A	12.6 Wh	High-capacity packs

Top Manufacturers and Models

There are dozens of "brands" of 18650/21700 cells on the market, but only a handful of genuine cell manufacturers.

Sony / Murata: VTC5A, VTC6, VTC6A — the gold standard for high-drain cells.

Molicel (E-One Moli Energy): Canadian manufacturer, supplier to Tesla and Dyson. P26A, P28A, P42A — outstanding current delivery.

Samsung SDI: 25R, 30Q, 40T, 50E — wide range from all-rounders to specialists.

LG Energy Solution: HG2 ("Chocolate"), MJ1 — popular and reliable.

Panasonic / Sanyo: NCR18650B, NCR18650GA — capacity record holders.

How to Spot Fakes

The 18650 market is flooded with counterfeits. "UltraFire 9800 mAh cells" for €2 are a scam. It's physically impossible to fit 9800 mAh into the 18650 format (the real maximum is around 3600 mAh).

Weight Test

The quickest check. A genuine 18650 cell weighs 44-50 grams. A fake typically weighs 25-35 grams. Kitchen scales with 1g accuracy are all you need.

Capacity Test

Fully charge the cell (4.20V) and discharge to 2.5V through a charger with capacity measurement (LiitoKala Lii-500, XTAR VC4). If actual capacity is less than 80% of the claimed figure — it's a counterfeit or a worn cell.

Visual Inspection

Originals have laser-engraved markings, even wrapping, crisp font.
Fakes — blurry printing, uneven heat shrink, no QR code.
Check the source — buy from trusted suppliers.

Cell Storage

Temperature: +10-25°C (ideally +15°C). Not in the fridge (condensation!), not in heat.
Charge level: 40-60% (3.6-3.8V). Don't store fully charged (4.2V) or fully discharged (below 3.0V).
Container: plastic case to prevent contact short-circuits (pockets, keys, coins).
Shelf life: with proper storage, cells lose 2-3% capacity per year.

Recycling and Safety

Lithium cells are hazardous waste. They must not go in general rubbish.

In Latvia: drop off at battery collection points in shops (Rimi, Maxima, Euronics) or at Getliņi.
Damaged cells (swollen, damaged wrapper, getting hot) are particularly dangerous. Place in sand or vermiculite and take to a specialist collection point.

At the SATER service centre, we build battery packs from tested cells (Sony, Molicel, Samsung, LG, Panasonic) and properly recycle old cells. If you need a power tool or robot vacuum battery repack, or a custom battery assembly — get in touch.