1Insulating ring
2+ terminal (button end)
3Li-ion cell 18650 (PVC sleeve) · Ø 18.5 × 69 mm (protected)

Cylindrical metal cell, colored plastic sleeve, protruding plus end, flat minus end
18 mm diameter × 65 mm long (shielded type slightly longer)

Power supply

Li-ion cell (18650)

In simple terms

What is this?

A strong rechargeable cylindrical battery; a big bucket of big energy.

What is it for?

Powers portable devices that need a lot of current, such as robots, flashlights and power banks.

Where do you see it?

Inside power banks, flashlights and laptop batteries.

How do you spot it?

A cylinder slightly thicker and longer than an AA battery; it has text on it and the plus end sticks out.

Caution:

Overcharge, deep discharge and short circuit can start a fire; do not use without a protection circuit, do not crush.

Technical definition

A rechargeable cylindrical cell in which lithium ions move back and forth between two electrodes. The name 18650 comes from its dimensions: 18 mm diameter, 65 mm length. It stores a lot of energy; always use it with a protection circuit (BMS) against overcharge, over-discharge and short circuit.

Nominal3.6–3.7 V

Full4.2 V

Capacitance1500–3500 mAh

Schematic symbol Same in IEC and ANSI

IEC 60617: the drawing style used in Türkiye and Europe.

Pins 2

1Plus (+)Protruding terminal+

2Minus (−)Flat end; the metal case is also negative−

Features typical

Nominal voltage: 3.6–3.7 V
Fully charged: 4.2 V
Cutoff voltage: 2.5–3.0 V
Capacitance: 1500–3500 mAh
Charge: CC/CV, up to 4.2 V (like the TP4056)
Max. current: Depends on the model; power cells 10 A and up
Protection: BMS required
Example part: Protected 18650 cell

Common mistakes

Causing a short circuitIf the terminals short out, a very large current flows; the cell can overheat and catch fire. Don't leave the terminals exposed or carry it in your pocket.

Charging with an unsuitable deviceA Li-ion cell is charged only with a CC/CV charging circuit, up to 4.2 V. Charging it directly from a simple adapter is dangerous.

Over-dischargingA cell that drops below 2.5–3.0 V is permanently damaged. Use a BMS or low-voltage cutoff.

Test with a multimeter

Test whether this part is good with the multimeter on the measurement screen.

Take a measurement

Where it is used

Portable robot and flashlightPower bankMicrocontroller sensor nodeBluetooth speaker