1. What an 18650 is
A cylinder about 18 mm wide and 65 mm long, with a rechargeable lithium-ion chemistry. It isn’t the same as a CR123A, though the two can look similar.
2. Buy protected cells
Choose cells with a built-in protection circuit, made for the device or sold by a reputable seller. Check the capacity and voltage printed on the label.
3. Use the right charger
Charge only with a charger that matches the cell type and voltage. Don’t charge a cell that is hot, damaged or swollen.
4. Keep them apart
Store cells in a plastic case, not loose in a pocket or bag with coins or keys. A short circuit can make a cell overheat quickly.