What Batteries Do Flashlights Use? AA to 18650 Explained
Our customer asked:
What batteries do flashlights use, and does it matter which one you buy?
TL;DR
Most flashlights use one of three groups of batteries. The first is standard 1.5-volt AAA, AA, C or D cells, alkaline or lithium. The second is 3-volt CR123A lithium cells, common in compact tactical lights. The third is rechargeable 3.6 to 3.7-volt lithium-ion cells such as the 18650, 21700 and 26650, either removable or built into the light. Which one a light uses decides how bright it can be, how long it runs, and what you will pay to keep it going.
I run product innovation at LUXPRO. We make lights in all three groups, so I have no reason to push you toward one. Here is how they compare and the mistakes I see most often.
Every common flashlight battery, compared
| Battery | Voltage | Rechargeable? | Best for |
|---|---|---|---|
| AAA | 1.5 V (1.2 V NiMH) | NiMH versions | Penlights, small headlamps, UV lights like our LP32UV |
| AA | 1.5 V (1.2 V NiMH) | NiMH versions | Everyday lights, headlamps, lanterns. Easy to find anywhere. |
| C | 1.5 V | Rarely | Older full-size lights and lanterns |
| D | 1.5 V | Rarely | Classic heavy flashlights, big lanterns |
| CR123A | 3.0 V | No (see 16340) | Compact tactical lights, backup power. Ten-year-class shelf life. |
| 18650 | 3.6 to 3.7 V | Yes | Most rechargeable flashlights |
| 21700 / 26650 | 3.6 to 3.7 V | Yes | High-output and long-runtime lights |
| Built-in Li-ion | Usually 3.7 V | Yes, via USB | Sealed everyday lights like our XP913 |
Voltage matters more than size
If you take one thing from this article, I want it to be this. A battery that physically fits is not necessarily safe to use. The flashlight's driver circuit is designed for a specific voltage range, and too much voltage can destroy it instantly.
- 14500 cells are the size of an AA but run at 3.7 V. Drop one into a light built for a single 1.5 V AA and you can burn out the LED or driver the moment you click it on. Only use them in lights that say 14500 is supported.
- RCR123A (also called 16340) cells are the size of a CR123A but run at 3.7 V, and up to 4.2 V when full. That is the honest answer to "Can I use a 3.7 V battery instead of a 3 V battery?": only if the manufacturer says the light accepts it.
- Two CR123As in series make 6 V. One 18650 makes 3.7 V. Some lights are designed to accept either. Our XP920 is one, because its driver is built to handle both ranges. You cannot assume that about a light that does not say so.
C vs. D, and what "D4" means
I get asked about C and D batteries a lot. Both are 1.5 volts. The D is larger and holds more energy, roughly half again to double what a C holds depending on the load. Because they are different sizes, you cannot swap one for the other without a spacer, and a C in a D-sized light gives you less runtime.
I see this one confuse people all the time: "D4" is not a different battery. It is packaging shorthand for a four-pack of D cells. The batteries inside are ordinary 1.5 V D cells, the same as a single D. Likewise, AA8 means eight AAs and AAA4 means four AAAs.
Alkaline vs. lithium vs. rechargeable
Alkaline is cheap and sold everywhere. Its weakness is high drain. A bright LED pulls hard enough that an alkaline's voltage sags, so the light dims well before the battery is truly empty. Alkalines can also leak if they sit for a long time, and leakage destroys more flashlights than drops do. If a light will be stored for months, take the alkalines out.
Lithium primaries (disposable lithium AA, AAA and CR123A) handle high drain better, work far better in the cold, weigh less, and keep most of their charge for many years. They cost more. They are the best disposable choice for an emergency kit or a light that lives in a cold truck.
Rechargeable lithium-ion gives the most light per charge and the lowest cost over time if you use the light regularly. I go through rechargeable chemistries in detail in What is the longest-lasting rechargeable battery?
Why we build dual-power lights
I will be honest: rechargeable lights have one real weakness: when the battery is flat and there is no outlet, you are out of light. Our answer is dual power, a rechargeable lithium-ion system that also accepts batteries you can buy at any gas station.
- XP920: one 18650, or two CR123As.
- XP713: two 18650s, or 9 AAA.
- XP715: two 26650s, or 9 AA through an included carrier.
- LP309: one or two 18650s, 4 AA, or USB-C power.
Backup batteries give lower output and runtime than the lithium-ion cells. I think that is a fair trade for never being left in the dark.
How to choose
- Used several times a week: rechargeable lithium-ion. See my 10 Best Rechargeable Flashlights comparison.
- Kept for emergencies: lithium primaries, or a dual-power light with lithium backups stored beside it.
- Everyday household lights: AA or AAA, with low-self-discharge NiMH rechargeables if you want to stop buying batteries.
- Kids' lights: AA or AAA. Keep loose lithium-ion cells away from children.
Frequently Asked Questions
Q: Are flashlight batteries C or D?
Some older full-size flashlights use C or D. Most modern LED flashlights use AA, AAA, CR123A or rechargeable lithium-ion cells such as the 18650.
Q: Are D4 batteries 1.5 V?
Yes. D4 just means a four-pack of standard 1.5 V D batteries.
Q: Can I use a 3.7 V battery instead of a 3 V battery?
Only if the flashlight manufacturer says it is supported. A fully charged 3.7 V lithium-ion cell reaches 4.2 V, which can damage lights designed for 3 V CR123A cells.
Q: What is an 18650 battery?
A cylindrical 3.7 V lithium-ion cell, 18 mm by 65 mm, used in most rechargeable flashlights. Details: What is an 18650 battery?
Q: Should I leave batteries in a flashlight I'm storing?
Not alkalines; take them out to prevent leaks. Lithium primaries are much less prone to leaking. For rechargeable lights, see Should you leave a rechargeable flashlight plugged in?