18650 Battery Guide: Size, Button Top vs Flat Top, Protected vs Unprotected

Quick answer: “18650” describes an approximate cylindrical cell size, but cells can differ in length, terminal style, protection circuit and discharge capability. Match all requirements of the device, not just the diameter.

Key differences

Button-top cells have a raised positive terminal; flat-top cells do not. Protected cells include an added circuit and are usually longer. A device designed for one format may not accept the other.

Before ordering

• Check device voltage and chemistry.
• Measure the existing cell length and diameter.
• Identify button top or flat top.
• Confirm protected or unprotected requirements.
• Check discharge-current requirements.
• Never use a cell with damaged wrapping.

Relevant products

• Single 18650 rechargeable battery
• Four-pack 18650 batteries
• Eight-pack 18650 batteries
• 18650 battery collection

FAQs

Are all 18650 batteries the same length?

No. Protection circuits and terminal styles can increase length.

Can I replace a button top with a flat top?

Only when the device manufacturer and contact design permit it.

Safety: Do not carry loose cells with metal objects or use torn, dented, wet or overheating cells.