18650 Battery Safety or Not

Safety Precautions

18650 batteries can short out and catch fire.
Use caution when working with and using lithium ion batteries as they are very sensitive to charging characteristics.
Charge only with a smart charger designed for this specific type of lithium ion battery.
Always charge in or on a fire-proof surface.
Never leave batteries charging unattended.

Misusing or mishandling lithium ion batteries can pose a serious risk of personal injury, property damage, or death.
Batteries may explode, burn, or cause a fire if misused or mishandled.
Only use with proper circuitry in a protected battery pack.
Only use within manufacturer listed specifications.
Do not store loose battery in a pocket, purse, etc. - always use a protective case or box.
Keep away from metal objects to prevent short circuiting.
Do not short circuit.
Do not use if wrapper or insulator is damaged or torn.
Do not use if damaged in any way.
Do not overcharge or over-discharge.
Do not modify, disassemble, puncture, cut, crush, or incinerate.
Do not expose to liquids or high temperatures.
Do not solder, spot weld only.
User must be familiar with handling lithium ion batteries before purchase.
Usage of batteries is AT YOUR OWN RISK.

Button tops are just that, a button or nipple looking thing on the end of the battery.
Protected and non-protected Li-ion has nothing to do with the physical + end contact.
There is no difference in risk between button top and flat top cells, all else equal.

Good practice is to use batteries with protection circuits.
There are button tops with protection, and without. There are flat tops with protection, and without.
A great follow up read is on protective circuits: Protection Circuits

- Sale price: $4.99

- Price: $9.99

Purchased a head lamp from Amazon with batteries that had no labeling, no identification, and no traceability.
Batteries had caps like a battery that has electronic protection but how could you know?
Good bet these are not protected just on cost. Quality protected ones are around $10 bucks.
Going through inventory of misc recovered batteries, it became evident that a lot had no identification and even removing the blue plastic cover revealed no traceability.

Constantly topping off charge for hours, days, and weeks is abuse and will only result in a reduction of cell capacity, current, and ability to hold charge.
Over-discharged cells below 2.5V for Li-ion (which with LiCo chemistry can cause them to explode or catch on fire if charging is subsequently attempted).
Do not mix and match old and new, used and unused batteries.

PRBA – The Rechargeable Battery Association applauds the Safety Warning issued by the U.S. Consumer Product Safety Commission (CPSC) regarding the safe use of 18650 lithium ion battery cells.
PRBA's policy on the use of these and other cylindrical lithium ion battery cells explains how manufacturers of these products never intended them to be sold to consumers as loose, replaceable power sources without the necessary safety protection features.