Olight makes some of the batteries and lights discussed here. Olight specs and regular prices come from its US product pages as of September 2026; other cells' figures come from their makers' datasheets. Energy, cost and percentage figures are calculations from those published numbers, not lab measurements.
⚡ TL;DR
In the 18650 vs CR123A vs 21700 vs AAA comparison, a 21700 lithium-ion cell stores the most energy, 16.2 to 18 watt-hours. A high-capacity 18650 stores about 12.6 Wh. A CR123A holds about 4.5 Wh but keeps for years and is rated to -40°F, and a AAA holds about 1 to 2 Wh. Use only the battery your flashlight's manual lists.
If you have ever stood at a battery rack wondering whether a CR123A can stand in for the 18650 in your light, or whether a bigger 21700 is worth the bulk, the labels won't help much. Cells that look alike run at different voltages, datasheets use different test conditions, and a wrong swap can damage a light. This guide compares the four sizes with makers' figures, shows the cost math and lists the rules for storing and flying with each.
This table compares one representative cell of each size in the 18650 vs CR123A vs 21700 vs AAA matchup, using the manufacturers' published datasheets.
| Battery | Example cell | Nominal voltage | Capacity | Energy | Rechargeable | Rated temperature |
|---|---|---|---|---|---|---|
| 21700 | Molicel INR-21700-P45B | 3.6 V | 4,500 mAh typical | 16.2 Wh | Yes | -40°F to 140°F discharge; 32°F to 140°F charge |
| 18650 | Molicel INR-18650-M35A | 3.6 V | 3,500 mAh typical | 12.6 Wh (calculated) | Yes | Not published on Molicel's product page |
| CR123A | Energizer 123 (EL123AP) | 3.0 V | 1,500 mAh typical | 4.5 Wh (calculated) | No | -40°F to 140°F |
| AAA | Panasonic eneloop (Ni-MH) | 1.2 V | Up to 800 mAh (750 mAh minimum) | 1.0 Wh (calculated) | Yes | -4°F to 122°F |
Calculated energy multiplies nominal voltage by capacity, the same watt-hour method the FAA gives in its guide for airline passengers and batteries. Each maker measures capacity under its own test conditions, so treat these energy figures as a rough guide to how much a cell holds, not as a runtime prediction for any particular light.
📋 Table of Contents
- 1. Which Flashlight Battery Lasts the Longest?
- 2. Flashlight Battery Types Explained: Size, Voltage and Chemistry
- 3. Can I Use 18650 Instead of CR123A?
- 4. Are 21700 Batteries Better Than 18650?
- 5. Why Do CR123A Batteries Still Make Sense?
- 6. What About AAA and AA Batteries?
- 7. Proprietary vs Standard Flashlight Batteries: What to Know
- 8. How Should You Store, Charge and Travel With Flashlight Batteries?
- 9. How Can You Tell if a Battery's Capacity Is Overstated?
- 10. Which Battery Should You Choose? A Quick Checklist
- 11. FAQ
Which Flashlight Battery Lasts the Longest?
That depends on what "lasts" means. Per charge, a 21700 lasts longest because it stores the most energy. In storage, lithium primaries lead: Energizer lists a 25-year shelf life at 21°C (70°F) for its lithium AA and AAA, and SureFire gives its 123A cells 10 years. For reuse, Panasonic rates eneloop for up to 2,100 recharges under a 2011 IEC method.
This table shows the published figure behind each kind of lasting, with the cell it comes from.
| Measure | Example | Published figure |
|---|---|---|
| Energy per battery | 21700 lithium-ion | 16.2 Wh for the Molicel INR-21700-P45B; 18.0 Wh calculated for Olight's 5,000 mAh, 3.6 V cell |
| Shelf life | Lithium primary AA and AAA | 25 years at 21°C (Energizer L91 and L92 datasheets) |
| Recharge cycles | Ni-MH (Panasonic eneloop) | Up to 2,100 under the IEC 61951-2:2011 method, or 600 under the 2017 method; makers use different tests, so cycle counts don't compare directly |
| Charge kept in storage (rechargeables) | Low-self-discharge Ni-MH (Panasonic eneloop) | 70% of minimum capacity after 10 years at 20°C, per Panasonic's estimate |
The shelf-life and cycle figures come from Energizer's L92 lithium AAA datasheet, SureFire's 123A battery page and Panasonic's eneloop specifications.
A flashlight's modes decide how that capacity is spent. The Olight Warrior 3S (2,300 lumens, 5,000 mAh 21700 battery) runs 200 lumens for 13 hours on Medium, while the Olight Baton 4 Pro (1,600 lumens, 3,500 mAh 18650 battery) runs 120 lumens for 18 hours 30 minutes. The smaller 18650 light lasts longer here only because its Medium mode is dimmer, so compare runtimes at the same output, not across different mode levels. For how rechargeable cells age over hundreds of cycles, see our guide to how long rechargeable flashlight batteries last.
Flashlight Battery Types Explained: Size, Voltage and Chemistry
Four sizes power most flashlights. The numbers in 18650 and 21700 describe the cell's dimensions, roughly 18 mm wide by 65 mm long and 21 mm by 70 mm. A CR123A is a 3-volt lithium cell about 17 mm wide and 34.5 mm long. AA and AAA cells come as 1.5-volt alkaline or lithium cells, or as 1.2-volt nickel-metal hydride (Ni-MH) rechargeables.
The chemistry, voltage, maximum size and weight of each type below come from the makers' datasheets and product pages.
| Battery | Chemistry | Nominal voltage | Maximum size | Weight |
|---|---|---|---|---|
| 21700 (Molicel INR-21700-P45B) | Lithium-ion | 3.6 V | 21.55 × 70.15 mm | 70 g maximum |
| 18650 (Molicel INR-18650-M35A) | Lithium-ion | 3.6 V | 18.6 × 65.2 mm | 48 g maximum |
| 16340 (Olight IMR16340) | Lithium-ion | 3.6 V | Not listed | Not listed |
| CR123A (Energizer 123) | Lithium manganese dioxide | 3.0 V | 17.0 × 34.5 mm | 16.5 g typical |
| AA lithium (Energizer L91) | Lithium iron disulfide | 1.5 V | 14.5 × 50.5 mm | 15 g typical |
| AA Ni-MH (Panasonic eneloop) | Nickel-metal hydride | 1.2 V | 14.5 × 50.5 mm | 27 g |
| AAA lithium (Energizer L92) | Lithium iron disulfide | 1.5 V | 10.5 × 44.5 mm | 7.6 g typical |
| AAA alkaline (Energizer E92) | Zinc-manganese dioxide | 1.5 V | 10.5 × 44.5 mm | 11.5 g typical |
| AAA Ni-MH (Panasonic eneloop) | Nickel-metal hydride | 1.2 V | 10.5 × 44.5 mm | 13 g |
Voltage matters more than size when you consider swapping one battery for another. A 21700 and an 18650 share the same 3.6-volt rating, so the difference between them is energy and bulk. A CR123A runs at 3.0 volts, a rechargeable 16340 at 3.6 volts and a AAA at 1.5 or 1.2 volts, so cells that look like they might fit a light often don't match its electronics.
This table explains each battery spec you will see on a datasheet, its unit, the range across the cells in this guide and how to tell whether a number is enough for your light.
| Spec | Unit | Range across the cells in this guide | How to tell if it is enough |
|---|---|---|---|
| Nominal voltage | Volts (V) | 1.2 V (Ni-MH) to 3.6 V (lithium-ion) | It must match what your flashlight's manual lists; more is not better |
| Capacity | Milliamp-hours (mAh) | 750 mAh minimum (eneloop AAA) to 5,000 mAh (Olight 21700) | Compare only within the same voltage; across voltages, use watt-hours |
| Energy | Watt-hours (Wh) = V × Ah | About 0.9 Wh (eneloop AAA, minimum) to 18 Wh (Olight 21700) | More watt-hours means longer runtime in the same light; the FAA's per-battery limit without airline approval is 100 Wh |
| Rated temperature | °F or °C | Down to -4°F (eneloop) or -40°F (lithium primaries, Molicel P45B discharge) | Choose a cell rated below the coldest temperature you will use it in |
| Shelf life | Years at a stated temperature | 10 years (Energizer E92, SureFire 123A) to 25 years (Energizer L91, L92) | For a kit you rarely check, pick the longest shelf life |
| Continuous discharge | Amps (A) | 1.5 A (Energizer 123 and L92) to 45 A (Molicel P45B) | Matters for high-output lights; follow the cell your flashlight maker lists |
Can I Use 18650 Instead of CR123A?
Only if your flashlight's manual lists both. The voltages don't line up: one 18650 is rated at 3.6 volts, one CR123A at 3.0 volts, and two CR123A cells in series at 6.0 volts. A light designed around one of those configurations isn't automatically built for the others, so a swap is supported only when the flashlight's maker names both options.
That voltage gap is the heart of the 18650 vs CR123A question, and the same caution applies to rechargeable CR123A substitutes. A 16340, often sold as an RCR123A, runs at a higher voltage: Olight's Baton 4 spec sheet lists its customized 650 mAh 16340 at 3.6 volts, against 3.0 volts in Energizer's 123 datasheet, so two 16340s in series supply about 7.2 volts where two CR123A cells supply 6.0. Each flashlight maker sets its own rule; SureFire's battery safety page, for its lights, says to "ONLY USE rechargeable LFP 123A batteries in SureFire LED illumination tools designed to be powered primarily by disposable 123A lithium batteries."
This table shows the common swap questions by what each light was designed for.
| Light designed for | Supplied voltage | What to use |
|---|---|---|
| One 18650 | 3.6 V | An 18650; two CR123A cells only if the manual lists them |
| Two CR123A cells | 6.0 V | Two CR123A cells; an 18650 or two rechargeable 16340s only if the manual lists them |
| One CR123A | 3.0 V | A CR123A; a 3.6 V 16340 only if the manual lists it |
| An Olight model with a customized cell | As listed by Olight | The Olight battery listed for that model |
Olight's own listings follow this rule. The Olight CR123A Battery (1,600 mAh, 3 V lithium) is listed for the PL Turbo, Baldr Pro, Baldr RL, Baldr IR, PL-3, PL-2, Valkyrie Turbo, S1R II, S1R and S1. The Olight IMR16340 Battery (650 mAh) is listed for the Baton 4, Baton 3, Perun 3 Mini, Perun 2 Mini and Perun Mini; Olight lists the 550 mAh version for the Baton 3, Perun 2 Mini and Perun Mini.
Are 21700 Batteries Better Than 18650?
A 21700 is better when you want more runtime and your flashlight is built for it. Molicel's INR-21700-P45B stores 16.2 watt-hours, about 29% more than the 12.6 watt-hours its INR-18650-M35A holds, but it weighs up to 70 grams against 48. An 18650 still makes sense when a smaller, lighter light matters more than runtime.
This table compares two cells from the same maker, using the figures in Molicel's P45B datasheet and on its M35A product page.
| Spec | Molicel INR-18650-M35A | Molicel INR-21700-P45B |
|---|---|---|
| Typical capacity | 3,500 mAh | 4,500 mAh |
| Energy | 12.6 Wh (calculated at 3.6 V) | 16.2 Wh |
| Maximum weight | 48 g | 70 g |
| Maximum size | 18.6 × 65.2 mm | 21.55 × 70.15 mm |
| Volumetric energy density | 730 Wh/L | 643 Wh/L |
| Continuous discharge | 10 A | 45 A (80°C cutoff) |
The 21700 holds more total energy but less per liter. The M35A packs about 14% more energy into each liter, so the 21700's advantage comes from its larger volume. The two cells also target different jobs: Molicel rates the P45B for 45 amps of continuous discharge and the M35A for 10 amps.
Olight's own cells show a wider gap. The Olight 21700 Rechargeable Battery (5,000 mAh, 3.6 V, $26.95, regular price, September 2026) holds about 43% more capacity than the Olight 18650 Battery (3,500 mAh, $18.95, regular price, September 2026). The trade-off shows up in the lights themselves: the 21700-powered Warrior 3S has a 29.5 mm body, while the 18650-powered Baton 4 Pro measures 23 mm across.
Why Do CR123A Batteries Still Make Sense?
CR123A cells make sense for lights that sit unused for long stretches or have to work in the cold. Energizer rates its 123 for use from -40°F to 140°F, SureFire gives its 123A cells a 10-year shelf life, and neither needs a charger. The trade-off is cost: each cell is used once and holds far less energy than an 18650.
Cold weather is where the chemistry differences show. Molicel's INR-21700-P45B is rated to discharge down to -40°F, but its datasheet limits charging to 32°F and above, and its temperature curves show lower voltage as the cell gets colder. Energizer's 123 datasheet gives a rating but no cold-weather curve; its L91 lithium AA datasheet, a different lithium chemistry, shows capacity at a 1,000 mA drain falling toward zero as temperatures approach -40°F, while a 25 mA drain barely changes. Alkaline AAAs are more limited still: Energizer rates its E92 for use from 0°F to 130°F.
Per watt-hour, CR123A cells cost less at purchase but can't be reused. The figures below use Olight's regular prices in September 2026 and each cell's nominal voltage and capacity.
| Battery | Regular price | Nominal energy | Price per watt-hour at purchase |
|---|---|---|---|
| Olight 21700 (5,000 mAh, 3.6 V) | $26.95 | 18.0 Wh | $1.50 |
| Olight 18650 (3,500 mAh, 3.6 V) | $18.95 | 12.6 Wh | $1.50 |
| Olight CR123A (1,600 mAh, 3.0 V) | $1.99 | 4.8 Wh | $0.41 per cell used |
| Ostation Ecolast AA (2,100 mAh, 1.5 V) | $16.99 for four | 3.15 Wh | $1.35 |
A rechargeable cell's price is paid once. One full charge of Olight's 21700 holds as much nominal energy as 3.75 of its CR123A cells, or $7.46 worth at $1.99 each, so the $26.95 cell has covered its price in energy terms by its fourth full charge. That math leaves out charger and electricity costs, and it compares energy only, since the two batteries power different lights.
If your CR123A light is part of a home outage kit, our guide to choosing an emergency flashlight plans the lights room by room.
What About AAA and AA Batteries?
AAA and AA cells suit small lights and households that already stock them. Lithium AAAs lead on storage and cold: Energizer's L92 datasheet lists a 25-year shelf life at 21°C and use from -40°F to 140°F. Alkaline AAAs are inexpensive but rated only down to 0°F, and rechargeable Ni-MH AAAs hold less energy because they run at 1.2 volts.
Drain rate changes the picture for alkaline cells. Energizer's E92 alkaline AAA datasheet shows its AAA delivering less than half as much capacity at a 500 mA drain as at 25 mA, which is why an alkaline AAA fades quickly in a bright light. Low-self-discharge Ni-MH cells keep much of their charge in storage: Panasonic estimates eneloop cells retain 70% of their minimum capacity after 10 years at 20°C. In AA size, Panasonic lists eneloop at up to 2,000 mAh, with a 1,900 mAh minimum.
Warning: Check the flashlight before switching to Ni-MH. Panasonic states that "eneloop cannot be used in devices with airtight battery compartments, such as water-proof flashlights," so read your light's manual for approved cell types.
For AA devices, the Ostation Ecolast 1.5V AA Battery (2,100 mAh, 1.5 V, 3,150 mWh; $16.99 for four, regular price, September 2026) is a lithium-ion AA with a battery management system in every cell. Olight rates it for more than 1,000 cycles and use from -4°F to 140°F. If a cell reaches its rated 1,000 cycles, its share of the four-pack price works out to less than half a cent per charge, before charger and electricity costs. The Olight Ostation 2 series stores up to 12 AA and 12 AAA cells and charges Ni-MH AA and AAA batteries plus Ecolast AAs; Olight says it fully charges batteries in as little as 2.5 hours. Its spec sheet lists two AA and two AAA cells charging at one time, so topping up a full rack takes several rounds. The Ostation 2 Pro, at $139.99 (regular price, September 2026), adds a 2.8-inch touchscreen and two MCC magnetic charging ports. On the flashlight side, the Olight i3E EOS (90 lumens, one AAA battery) is a keychain light that Olight says runs on "a single widely available AAA battery." Its user manual says its specification tests were "performed with one GreenMax AAA Alkaline or eneloop pro NiMH Battery," so Olight rates it on both chemistries.
Proprietary vs Standard Flashlight Batteries: What to Know
Some Olight lights use cells made for specific models. Olight describes its 5,000 mAh 21700 as a "Customized rechargeable 21700, 5000mAh 3.6v Battery specifically designed for" lights including the Warrior 3S and Seeker 4 Pro, and its store listing names its 3,500 mAh 18650 a "customized" battery for lights such as the Warrior Mini 3 and Perun. A same-size standard cell is not automatically a substitute.
The practical cost of a customized cell is sourcing. A replacement has to match the model Olight lists for your light, so a spare is worth buying before a long trip or a storm season. Cells sold under the same size name can also differ in ways the label doesn't show; the CPSC notes, for example, that 18650 cells pulled from battery packs "do not have protection circuits." Olight's product pages list which lights each battery fits, and together with the manual, that listing is the rule to follow.
This table lists the Olight batteries covered in this guide and the lights each one is listed for.
| Olight battery | Key specs | Regular price (September 2026) | Listed for |
|---|---|---|---|
| 21700 Rechargeable Battery | 5,000 mAh, 3.6 V, customized | $26.95 | Warrior Ultra, Warrior 3S, Warrior X 4, Seeker 4 Pro, Perun 3, Odin and other models |
| 18650 Battery | 3,500 mAh; listed as customized | $18.95 | Warrior Mini 3, Warrior Mini 2, Perun, Baton Pro, S2R Baton and other models |
| IMR16340 Battery | 650 mAh, 3.6 V; a 550 mAh version is also listed | $5.95 (550 mAh version) | Baton 4, Baton 3, Perun 3 Mini, Perun 2 Mini, Perun Mini |
| CR123A Battery | 1,600 mAh, 3 V lithium, 16.3 g | $1.99 | PL Turbo, Baldr Pro, Baldr RL, Baldr IR, PL-3, PL-2 and other models |
| Ostation Ecolast AA | 2,100 mAh, 1.5 V, 3,150 mWh | $16.99 for four | AA devices; charged by the Ostation 2 series |
This table sets six common battery beliefs against what the makers and regulators actually publish.
| Misconception | Fact | Basis |
|---|---|---|
| Same size means interchangeable | Olight lists its 21700 and 18650 as customized cells for named models, and loose 18650s pulled from packs lack protection circuits | Olight product pages; CPSC |
| A 21700 always beats an 18650 | The 21700 holds more total energy, but the M35A 18650 stores more per liter (730 vs 643 Wh/L) | Molicel figures |
| Only CR123A cells work in deep cold | Molicel's P45B is rated to discharge at -40°F, though it can't be charged below 32°F | Molicel P45B datasheet |
| More mAh always means more energy | A 1,500 mAh CR123A at 3.0 V holds 4.5 Wh; an 800 mAh eneloop AAA at 1.2 V holds about 1.0 Wh | Watt-hours = volts × amp-hours (FAA method) |
| A CR123A can be recharged | SureFire says to "NEVER attempt to recharge a disposable 123A lithium battery" | SureFire battery safety page |
| Spare lithium cells can go in a checked bag | Spare lithium-ion and lithium metal batteries go in carry-on baggage only | FAA PackSafe |
Browse all flashlight batteries and chargers to match a spare to your light.
How Should You Store, Charge and Travel With Flashlight Batteries?
Store lithium-ion cells partly charged in a cool place, carry spares with terminals covered, and pack spare lithium batteries only in carry-on bags when you fly. Battery University estimates that a lithium-ion cell kept a year at 40% charge and 77°F keeps 96% of its capacity as recoverable, against 80% when stored fully charged.
This table shows Battery University's storage estimates of recoverable capacity for a lithium-cobalt cell, and how temperature and charge level interact.
| Storage temperature | Estimated capacity at 40% charge | Estimated capacity at 100% charge |
|---|---|---|
| 32°F (0°C) | 98% after 1 year | 94% after 1 year |
| 77°F (25°C) | 96% after 1 year | 80% after 1 year |
| 104°F (40°C) | 85% after 1 year | 65% after 1 year |
| 140°F (60°C) | 75% after 1 year | 60% after 3 months |
Handling rules come from the battery and flashlight makers and from federal safety agencies:
- Keep loose cells away from metal. The U.S. Consumer Product Safety Commission, in its warning on loose 18650 cells separated from battery packs, says they "may have exposed metal positive and negative terminals that can short-circuit when they come into contact with metal objects, such as keys or loose change in a pocket."
- Don't mix batteries. Streamlight's battery information page warns that "mixing of used and new or different brand batteries may present a risk of leakage, fire, explosion and serious personal injury," and SureFire tells owners to replace all batteries at the same time and never load them backward.
- Never recharge disposable cells. SureFire tells owners to "NEVER attempt to recharge a disposable 123A lithium battery" and to charge lithium-ion and LFP 123A cells only with their designated chargers.
- Charge within the rated range. Molicel's INR-21700-P45B datasheet lists a 4.2-volt charge voltage and a charging range of 32°F to 140°F. Follow the charging temperature range in your flashlight's or charger's manual, and don't charge outside it.
- Retire damaged batteries. The FAA notes that thermal runaway "can occur without warning" if a battery is damaged, overheated, exposed to water, overcharged or improperly protected, and it bars damaged or recalled batteries, and devices that contain them, from carry-on and checked bags unless the battery has been removed or otherwise made safe.
Safety note: If a lithium-ion cell is dented, swollen, leaking or hot to the touch, stop using it and don't charge it. The FAA's rule above keeps such batteries off aircraft for the same reason: damage can lead to thermal runaway without warning.
Air travel has its own rules. This table summarizes the FAA's PackSafe lithium battery page (last updated August 11, 2026) and its passenger battery guidance (last updated August 10, 2026).
| Item | FAA rule |
|---|---|
| Spare lithium-ion and lithium metal batteries | Carry-on baggage only |
| Lithium-ion size | Up to 100 Wh per battery; up to two spares of 101 to 160 Wh with airline approval; over 160 Wh forbidden |
| Lithium metal size | Up to 2 grams of lithium per battery; 2 to 8 grams with airline approval |
| Flashlight with a lithium-ion battery installed | Same watt-hour limits as spares; can be checked only when powered off and protected from short circuit and unintentional activation |
| Alkaline and Ni-MH cells (AA, AAA) | Carry-on or checked, protected from damage and short circuit |
| Terminals | Protected from short circuit, such as in retail packaging, with tape or in a battery case |
| Bags checked at the gate | Spare lithium batteries must be removed and kept in the cabin |
Typical flashlight cells fall well under those limits. Molicel rates its INR-21700-P45B at 16.2 watt-hours, about 16% of the 100 Wh limit, and Energizer lists 0.55 grams of lithium in its 123 cell, about 28% of the 2-gram limit. The FAA notes that many airlines set stricter limits, so check with your carrier before you fly.
How Can You Tell if a Battery's Capacity Is Overstated?
Compare the label with the maker's datasheet and, if you have the equipment, run a controlled discharge. Molicel, for example, lists 4,500 mAh typical and 4,300 mAh minimum for its INR-21700-P45B, and its curves show a charge to 4.2 volts, a discharge to 2.5 volts and a 73°F ambient. A label far above datasheet figures is a warning sign.
A capacity check at home follows the same logic as a datasheet test:
- Find the rated capacity and its conditions: minimum capacity, cutoff voltage, discharge current and temperature.
- Use a charger or battery analyzer with a capacity-test mode made for that chemistry, and don't test a cell that is dented, swollen or leaking.
- Charge fully to the maker's charge voltage, 4.2 volts for the Molicel INR-21700-P45B.
- Discharge at a low, constant current at room temperature, and never below the maker's cutoff voltage. Molicel's P45B curves include a 0.2C discharge at 73°F.
- Compare the result with the minimum rating, keeping in mind that home analyzers and datasheet tests differ, so treat the comparison as a rough check.
A few warning signs make a closer look worthwhile. An 18650 labeled far above the capacities major cell makers publish, such as the 3,500 mAh Molicel lists for its INR-18650-M35A, deserves suspicion. So does an 18650 pulled from a battery pack and resold as a loose cell, the kind the CPSC tells consumers not to buy or use. Standardized test methods also exist for household rechargeables; Panasonic, for example, states eneloop capacity under the IEC 61951-2 method.
Which Battery Should You Choose? A Quick Checklist
Settle the 18650 vs CR123A question by what your flashlight's manual lists first, then by how you use the light. The steps below turn this guide's tables into a short decision path, so you can choose between an 18650, a CR123A, a 21700 and a AAA in a few minutes and avoid the swaps that damage lights.
- Read the manual or the maker's battery listing for your light, and use only the cells it names.
- If the light allows a choice, compare watt-hours, not milliamp-hours.
- For a light you use every week, choose a rechargeable 18650 or 21700 and store it partly charged in a cool place.
- For a light you rarely check or use in deep cold, choose lithium primaries such as CR123A or lithium AAA.
- Keep spare cells in a case or their retail packaging, and carry spare lithium cells in your carry-on when you fly.
- Retire any cell that is dented, swollen, leaking or unusually hot.
Once you know which battery fits your needs, compare lights built around each size in our guide to the best flashlights.
FAQ
Changelog
- September 25, 2026: Rewrote this guide with manufacturer datasheet figures, cost-per-watt-hour math, current FAA travel rules and Olight's current battery listings. First published June 16, 2026.
