| AA alkaline | About 2,000–2,800 mAh per cell; usable capacity varies with load and temperature | About 1–3 hours in a compact flashlight using one or two cells | About 20–60 hours, depending on the light’s low mode | Replace with widely available disposable AA cells; no built-in charging required | Occasional use, emergency kits, and trips where replacement cells are easy to find | Simple to replace, but performance can drop quickly under high loads and in cold conditions. Do not recharge disposable alkaline cells. |
| AA NiMH rechargeable | Typically about 1,900–2,500 mAh per cell | About 1–3 hours in a compact flashlight using one or two cells | About 20–60 hours, depending on the light’s low mode | Recharge in a compatible external NiMH charger; carry spare charged cells for longer trips | Frequent use when standard-size replacement cells are preferred | Can reduce disposable-cell waste. Check the flashlight manual for compatibility because cell voltage and performance may differ from alkaline cells. |
| CR123A lithium primary | About 1,400–1,700 mAh per cell; non-rechargeable | About 1–3 hours with a compatible high-output flashlight | About 20–50 hours, depending on the light’s low mode | Replace with new CR123A cells; rechargeable RCR123A cells are not interchangeable unless the flashlight specifically supports them | Cold-weather use, long-term storage, and compact lights designed for these cells | Good shelf life and cold-weather performance, but replacement cells may be less common and more costly than AA cells. |
| 18650 rechargeable Li-ion | Typically about 2,500–3,500 mAh per cell | About 1.5–4 hours at a sustained high setting | About 30–100 hours, depending on the light’s low mode | Charge in the flashlight if it has a protected charging port, or use a compatible external charger | Regular hiking, camping, and general-purpose outdoor use | Offers a useful balance of capacity and size. Use only the cell type and charging method specified by the flashlight manufacturer. |
| 21700 rechargeable Li-ion | Typically about 4,000–5,000 mAh per cell | About 2–5 hours at a sustained high setting | About 40–120 hours, depending on the light’s low mode | Charge through a compatible built-in port or with an external charger designed for the cell | Longer outings and users who want greater capacity in a single-cell flashlight | Usually larger and heavier than an 18650 cell. High-output modes may cause the flashlight to reduce brightness as it heats up. |
| Built-in rechargeable Li-ion battery | Commonly about 1,000–5,000 mAh, depending on flashlight size | About 1–4 hours at a sustained high setting | About 20–100 hours, depending on the light’s low mode | Recharge through the flashlight’s USB port; some models also support charging from a power bank | Convenient everyday carry and trips with access to USB power | Easy to recharge, but the battery may not be user-replaceable. Check charging-port protection and whether the light can operate while charging. |