The numbers are dimensions: an 18650 is 18mm wide and 65mm long; a 21700 is 21mm wide and 70mm long. The larger 21700 typically holds more energy, often around 4,000 to 5,000mAh versus about 2,500 to 3,500mAh for an 18650, so it runs a light longer. Use only the cell type, size, and top style your flashlight specifies, and carry spares in carry-on luggage when flying.
- 18650 and 21700 are sizes, not brands or quality levels.
- Only use the cell your light is designed for, including button or flat top.
- Watt-hours = volts × amp-hours; a 3.6V 3,000mAh cell holds about 10.8Wh.
- Spare lithium batteries go in carry-on bags, with terminals protected.
What the numbers mean
| Cell | Size | Typical capacity | Typical use |
|---|---|---|---|
| 18650 | 18 × 65mm | about 2,500 to 3,500mAh | Compact tactical and hunting lights |
| 21700 | 21 × 70mm | about 4,000 to 5,000mAh | Brighter, longer-running lights |
| 14500 | 14 × 50mm | about 700 to 1,000mAh | AA-size EDC lights |
All three are lithium-ion cells with a nominal voltage of about 3.6 to 3.7 volts.
Capacity and real runtime
Capacity in milliamp-hours tells you how much charge a cell holds. To compare cells or lights fairly, convert to watt-hours: multiply the nominal voltage by the amp-hours. A 3.6V, 5,000mAh 21700 holds about 18Wh; a 3.6V, 3,000mAh 18650 holds about 10.8Wh.
More capacity means longer runtime at the same output, but high modes still drain any cell quickly and often step down to manage heat.
Charging and storage
- Use the right charger. Charge in the light over USB-C if it supports it, or in a dedicated lithium-ion charger.
- Do not leave charging unattended on soft surfaces or in hot cars.
- Store partly charged. For long storage, keep cells around half charged in a cool, dry place.
- Retire damaged cells. Recycle any cell with a torn wrap, dents, swelling, or heat while charging.
Flying with flashlight batteries
Under US FAA rules and those of most airlines, spare lithium-ion batteries must travel in carry-on luggage, not checked bags, with terminals protected from short circuits by the original packaging, a case, or tape. Cells installed in a flashlight can usually go in either bag, though carry-on is safer. Flashlight cells are far below the 100Wh per-battery limit, but check your airline before you fly.
A few good questions.
Can I use a 21700 in an 18650 flashlight?
No. A 21700 is wider and longer and will not fit. Some 21700 lights accept an 18650 with an adapter sleeve; check your manual.
Which lasts longer, 18650 or 21700?
A 21700 usually lasts longer because it holds more energy, often around 4,000 to 5,000mAh compared with about 2,500 to 3,500mAh for an 18650.
Are protected 18650 batteries better?
They add a safety circuit and suit lights without built-in protection. Many modern lights include protection and specify unprotected cells; follow the manual.
Can I bring 18650 batteries on a plane?
In the US, spare lithium-ion batteries must go in carry-on bags with terminals protected. Installed batteries can usually stay in the flashlight. Check your airline's rules.
Gear that helps.
Imalent BL70 6,000-Lumen EDC Flashlight
Best forCampers, hikers and tradespeople who want a very bright, rechargeable flashlight with a red light option and an OLED readout
A CREE XHP70.2 flashlight with up to 6,000 lumens, a red light source, an OLED display, a 3,000mAh rechargeable battery and Type-C fast charging.
Save about $7.99 with SEBASTIANBASSOL. Price checked October 27, 2026 · Imalent store · Store price; tax and shipping shown at checkout.
Imalent HT50 3,000-Lumen Dual Light Source Rechargeable Headlamp
Best forHikers, campers and night workers who want a bright, long-running headlamp with a red light option
A CREE XHP50.3 HL headlamp with up to 3,000 lumens, a 318 m beam, a 5,000mAh battery rated up to 350 hours, red and white light and Type-C charging.
Save about $5.99 with SEBASTIANBASSOL. Price checked October 27, 2026 · Imalent store · Store price; tax and shipping shown at checkout.
Imalent MS32 200,000-Lumen Flashlight
Best forSearch-and-rescue volunteers, cavers and enthusiasts who want the brightest consumer flashlight and can handle a large light
A 200,000-lumen searchlight with a 1,618 m beam, an OLED display, a replaceable battery pack that charges in about two hours over Type-C PD100W and a power bank function.
Save about $74.99 with SEBASTIANBASSOL. Price checked October 27, 2026 · Imalent store · Store price; tax and shipping shown at checkout.
UltraFire UF3 PRO Tactical Flashlight
Best forHikers and campers who want a bright rechargeable handheld with quick tail-switch activation and an included holster
We recommend the UltraFire UF3 PRO for hikers and campers who want a quick-on handheld beam and a rechargeable battery in the box. Its dual-switch controls and included holster are the practical draw; the 1,800-lumen high mode automatically steps down after three minutes.
Save about $3.20 with SEBASTIANBASSOL. Price checked October 16, 2026 · UltraFire US store · Current store sale price; final tax and shipping are determined at checkout.
UltraFire LR20X PRO Red
Best forNight hunters and ranchers who want a long-reaching red beam that is less likely to spook game
A rugged, waterproof red LED hunting light with a 350-meter throw. The 200-lumen red beam is built for scanning fields and fence lines at night without the glare of white light.
Price today $46.99 · Partner code lists 8% off; product eligibility is not listed.
Price checked October 17, 2026 · UltraFire US store · Bundle 1 sale price (list $59.99); Bundle 2 with mounts and remote switch is $109.99. The partner record does not list product eligibility.
UltraFire C15S 365nm UV
Best forHunters who want a filtered UV light for following a blood trail after the shot
A filtered 365nm UV flashlight built for one job: making blood drops stand out on leaves, grass, and soil when you recover game after dark. It ships ready to go with an 18650 battery and USB-C charging.
Price today $46.99 · Partner code lists 8% off; product eligibility is not listed.
Price checked October 17, 2026 · UltraFire US store · Store sale price (list $56.99); tax and shipping shown at checkout. The partner record does not list product eligibility.
UltraFire T5 1800 Lumen
Best forHikers and campers who want a bright, waterproof, USB-C rechargeable flashlight at a low price
A 135mm, 131g flashlight that UltraFire lists at 1,800 lumens, 276 meters, IP68 waterproofing, USB-C charging, and a tail switch plus side mode switch, running on a protected 18650.
Price today $34.99 · Partner code lists 8% off; product eligibility is not listed.
Price checked October 17, 2026 · UltraFire US store · Store sale price (list $46.99); tax and shipping shown at checkout. The partner record does not list product eligibility.
UltraFire LRS2 LEP
Best forHunters, property owners, and campers who want to see far down a field, ridge, or road at night
A 234g laser excited phosphor flashlight that UltraFire lists at 650 lumens, 717,824 candela, and a 1,695-meter beam, running on one 21700 with USB-C charging and IP68 protection.
Price today $125.99 · Partner code lists 8% off; product eligibility is not listed.
Price checked October 17, 2026 · UltraFire US store · Store sale price (list $179.99); tax and shipping shown at checkout. The partner record does not list product eligibility.
UltraFire WF-502B
Best forHikers, campers, and glove-box carriers who want a bright, simple flashlight at a very low price
A 109g aluminum flashlight with an UltraFire V6 LED rated at 1,000 lumens and 200 meters, running on one 18650 or two 16340 cells, sold in 1-mode and 5-mode versions with an optional holster package from $19.99.
Price today $19.99 · Partner code lists 8% off; product eligibility is not listed.
Price checked October 17, 2026 · UltraFire US store · Store price (list $22.99); the 5-mode version is $20.99 and packages with a holster are $27.99 and $28.99. Tax and shipping shown at checkout. The partner record does not list product eligibility.
UltraFire 502UV
Best forHunters, campers, and pet owners who want a low-cost 395nm UV light with an adjustable beam
A 3W 395 to 405nm UV flashlight with a zoomable beam, a 60 meter maximum beam distance, an IPX7 rating, and an 18650, 16340, or CR123A power option, from $17.99.
Price today $17.99 · Partner code lists 8% off; product eligibility is not listed.
Price checked October 17, 2026 · UltraFire US store · Store price (list $23.99); the package with an 18650 battery and DX-3 charger is $31.99. Tax and shipping shown at checkout. The partner record does not list product eligibility.
SOFIRN SC28 Powerful Tactical Flashlight
Best forHikers and vehicle-kit owners who want a compact single-beam light with a tail switch and 21700 battery
A 2,800-lumen single-beam flashlight with 21700 power, USB-C charging, a momentary-on tail switch, and an IPX8 rating.
Price today $28.36 · Free shipping with the code.
Price checked October 21, 2026 · SOFIRN US store · Store price (list $39.99); tax and shipping shown at checkout.
Imalent SR16 55,000-Lumen Rechargeable Searchlight
Best forSearch and camp users who want a large rechargeable light with a long-range beam and several lower modes
The SR16 combines 16 LEDs, a 55,000-lumen maximum, a four-cell battery pack, and lower modes with longer listed runtimes.
Save about $36.99 with SEBASTIANBASSOL. Price checked October 25, 2026 · Imalent store · Store price; tax and shipping shown at checkout.
Lumintop THOR III LEP Long-Range Flashlight
Best forExperienced light users who need a compact long-range beam and understand its narrow use case
The THOR3 pairs a 40-to-400-lumen LEP beam with a 2,500-meter listed throw and a rechargeable 21700 cell.
Save about $16.29 with SEBASTIANBASSOL. Price checked October 25, 2026 · Lumintop store · Store price; tax and shipping shown at checkout.
Imalent MS03 13,000-Lumen Rechargeable Flashlight
Best forCampers and search users who want a high-output handheld light with an included rechargeable 21700 battery
The MS03 pairs three Cree XHP70.2 LEDs with a 13,000-lumen maximum and a USB-C rechargeable 21700 battery.
Save about $12.99 with SEBASTIANBASSOL. Price checked October 25, 2026 · Imalent store · Store price; tax and shipping shown at checkout.
Lumintop EDC20 Compact Flashlight
Best forHikers and everyday carriers who want a short rechargeable flashlight with several white-light modes
The EDC20 pairs an 81mm body with a 2,000-lumen maximum, USB-C charging, and eight modes.
Save about $4.99 with SEBASTIANBASSOL. Price checked October 25, 2026 · Lumintop store · Store price; tax and shipping shown at checkout.
Lumintop FW3A Aluminum EDC Flashlight
Best forFlashlight users who want a compact 18650 light with a configurable ramping interface
The aluminum FW3A uses three LEDs, Andúril controls, and a 2,800-lumen maximum.
Save about $4.89 with SEBASTIANBASSOL. Price checked October 25, 2026 · Lumintop store · Store price; tax and shipping shown at checkout.
Lumintop W3 Mini LEP Flashlight
Best forCampers and hikers who want a small handheld that combines a focused spot with close-area flood and red light
The Lumintop online store calls this the W3 Mini, while Lumintop's manufacturer page names the model W3. The matching 700m LEP, 550-lumen combo, 79mm length, and 88g listed weight support treating the pages as the same model.
Price today $119.95 · 10% off with the code.
Price checked October 28, 2026 · Lumintop US store · The store page and Black variant feed agree on the listing price; tax and shipping are shown at checkout. Confirm the final order summary.
Lumintop Tool AA 3.0 EDC Flashlight
Best forEveryday carry kits that want a rechargeable 14500 light with a common AA-cell fallback
A compact 89.5mm flashlight that accepts either a 14500 rechargeable cell or one AA alkaline or Ni-MH cell, with a manufacturer-stated 900-lumen maximum on 14500 and 300 on AA.
Price today $25.95 · 10% off with the code.
Price checked October 28, 2026 · Lumintop US store · Store page and product feed list $25.95; tax and shipping are shown at checkout.
Lumintop D2 21700 Rechargeable Outdoor Flashlight
Best forCampers and hikers who want a 21700 flashlight with in-body USB-C charging and a magnetic tail cap
The selected green D2 option is named for a 21700 battery and supports built-in USB-C charging. Lumintop lists a 115mm body at about 85g without a cell, but its OSRAM and Nichia output tables are not mapped to the store's color and battery options.
Price today $39.99 · 10% off with the code.
Price checked October 28, 2026 · Lumintop US store · The official store page and product feed list this option at $39.99; tax and shipping are shown at checkout. Availability is not claimed. SEBASTIANBASSOL gives 10% off. Compare the final order total before payment.
Our approach
Written by Outdoor Gear Verdict Editorial. Grounded in lithium-ion cell standards and US FAA guidance on carrying batteries. Always follow local regulations and the manufacturer instructions for your equipment. Read our editorial standards.
