Li-Ion cells are made with flat tops and without protection. Some resellers add a protection circuit that guards against over charging, short circuits, and running the cell down too far. Usually when a protection circuit is added a button top is added to the cell as well. Also, the addition of the protection circuit adds slightly to the length of the cell, as well as its diameter. This means that a protected cell might not fit where an unprotected cell would.
Most protection circuits will shut off if more than three amps is attempted to be pulled from the cell. Some lights and other uses such as vapping require more than three amps, so unprotected cells must be used. Since there is no low voltage cut off without a protection circuit, it is the users responsibility to make sure the cell is not drawn down too far. Draining a cell below 3v will shorten a cell's life, and may physically damage the cell. Also, since there is no overcharge protection with an unprotected cell, a good charger is a must - one that will not overcharge the cell.
Li-Ion cells are touchy beasts. Over charging, over discharging (shorting, etc) can cause a cell to overheat and vent very noxious fumes. Draining a cell too low will shorten a cells life, and if low enough, will cause physical changes in the cell that can lead to internal shorts in the cell, which leads to outgassing, and possible explosions. A good, reliable volt meter is a must when working with Li-Ion cells to allow monitoring the cell voltage to determine when to recharge, and to keep from draining the cell to far down.
There is a section in the Battery University on the care and feeding of Li-Ion cells, and many threads here on CPF with good advice as well. Look at those, and feel free to ask any questions you may have here in the Forum. Remember, the only foolish question is the one unasked.
