My-STUFF 2017
18650 (3.7V, 9900mAh)
Actual Capacity: 1200mAh (As Tested)

Rechargeable Li-ion Battery
with a USB Battery Charger
18650(3.7V, 9900mAh)
ReChargeable Li-Ion Battery
Model: GTF 18650
Nominal Capacity: 1200mAh
Type: Li-Ion
Voltage: 3.7V
Size:18 x 65mm
Don't Open,
Don't Heat,
Don't Short Circuit,
Don't reverse,
Don't mix batteries.
USB Cable Charger
for 18650
Socket: USB
Brand Name: Binmer
Use: Standard Battery
Quick charge: No
Model: Charger
Socket Standard: USB
Colour: Black
Material: Metal & Plastic
Weight: 36g
3.5mm USB cable & charger
What is a 18650, in the world of Lithium-ion batteries?
The Answer:
18  The first two digits "18" stand for li-ion battery diameter in millimeters. In this case width of the battery is 18mm.
65  The third, and fourth digit stand for length in millimeters. That would be 65mm.
0?  For those who want to know why zero is there, this is how battery manufacturers calculate battery lengths: 650 divided by 10 is 65mm.
'18650' battery size dimensions: 18mm by 65mm = '18650'
The Metric system(millimeters) is used almost always when we see li-ion battery with numbers like: 18650, 18500, 16340, 16650, 14500 & 26650. These are the most common li-ion battery sizes. So, now when you see '18650' battery, you'll know the meaning of all those numbers.
Important: Battery dimensions in the real world can, and will vary.