commonly used in flashlights, battery packs, and specialty electronics.
The number is actually a dimension code:
-
18 = 18 mm diameter
-
50 = 50 mm length
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The final 0 = cylindrical cell shape
So an 18500 cell is 18 mm wide and 50 mm long.
18500
18500 Rechargeable Li-ion Battery 3.7v 1400mAh -Flat Top
$5.29 $5.29 / item
IFR18500 Lithium Iron Phosphate 3.2V Rechargeable Battery (8 Pack)
$27.29 $3.41 / item
Camelion 18500 LiFePO4 Rechargeable Battery 1000mAh (4 Pack)
$13.95 $3.49 / item
ICR18500 Button Top 1400mAh 3.7V Li-Ion Rechargeable Battery (4 Pack)
$18.95 $4.74 / item
Sanyo UR14500AC Battery 3.7v Li-Ion Flat-Top IO4 IO5 IO6 IO7 IO8 IO9 Replacement (2 Pack)
$18.49
Panasonic NCR18500A 2040mAh 3.8A 18500 Battery
$5.49 - $5.69
Vapcell N20 18500 2000mAh 10A 18500 Battery (Flat or Button Top) Bulk
$4.09 - $4.29$4.09 / item
Vapcell L22 18500 2200mAh 4A (Button Top or Flat Top) Battery
$4.49 - $4.69$4.49 / item
Vapcell N24 18500 2400mAh 5A 18500 Battery
$4.59 - $4.79
Vapcell N26 18500 2600mAh 5A 18500 Battery (Flat top or Button Top)
$4.79 - $4.99
Certified Hohm Tech 18650 Batteries
Hohm Tech Life V4 18650 Battery 3.6v 3015mAh 22.1A
$9.95 $7.89 $7.89 / item
Pre-Order Available 
Hohm 18650 Work V2 2547mAh 25.3A Battery
$9.95 $6.95 $6.95 /
Hohm Alone 18650 Battery 3.7v 3309mAh 15.3A ICR
$12.49 $8.99 $8.99 / item
Hohm Tech Mega 3.6v 18650 Rechargeable Battery – 2505mAh, 22A High Drain Li-ion Flat Top
$12.99 $7.79 $7.79 / item
Hohm Depot 18650 Battery 3.7v 16.8a 3005mAh (Flat Top)
$11.49 $7.99 $7.99 / item
Popular 21700 Options
Take a look at what fits the job for most
