3.7V Li-Ion Rechargeable Battery

The UltraFire 18650 is a 3.7V lithium-ion rechargeable battery built for high-drain devices — tactical flashlights, stun batons, and other electronics that demand consistent power output rather than the declining voltage curve of standard alkaline batteries. The 4000mAh capacity keeps devices running longer than competing 18650 cells, and the built-in PCB protection cuts off the battery if voltage drops below 2.5V or exceeds 4.25V, preventing both over-discharge damage and overcharge risk. Button top terminal, 500 charge cycles rated. Sold as a single battery.

UltraFire 18650 Battery Features and Specs

• Capacity: 4000mAh — higher energy density than competing 18650 rechargeable cells
• Nominal voltage: 3.7V, button top terminal
• PCB protection: Cuts off at 2.5V under-voltage and 4.25V over-voltage — protects both the battery and the device
• 500 charge cycles: 90% of initial capacity retained at 400 cycles
• Internal impedance: ≤180 milliohms
• Dimensions: 66.0mm x 18.0mm — Weight: 26.5g
• 3-year shelf life
• IEC standard tested: International Electrotechnical Commission testing for capacity, quality, and lifespan
• Color: may vary from image shown

The PCB (printed circuit board) protection is the practical safety feature that separates a protected 18650 from an unprotected cell. Unprotected 18650 batteries can be over-discharged into a state that makes them unsafe to recharge, or overcharged to the point of heat generation and potential failure. The PCB monitors voltage in real time and interrupts the circuit before either threshold is reached — the battery simply stops delivering or accepting charge rather than continuing into an unsafe range. For stun batons and tactical flashlights where the battery is relied upon for self-defense use, a protected cell is the right choice.

18650 Battery for Stun Guns and Tactical Flashlights

The 18650 format is the standard rechargeable cell for stun batons, tactical flashlights, and many high-drain portable devices. The 66mm x 18mm dimensions and 3.7V nominal voltage are the defining specs — any device that accepts 18650 batteries will accept this cell regardless of the original brand. For stun baton users replacing a worn battery, the 4000mAh capacity and PCB protection make this a direct upgrade over lower-capacity unprotected cells that may have shipped with the original unit. Compatible devices include emergency lighting, tactical LED flashlights, portable devices, and power tools using the 18650 format.

What does 18650 mean for a battery?

18650 is a size designation for a cylindrical lithium-ion battery cell — 18mm in diameter and 65mm in length, with the 0 indicating cylindrical format. It's the same naming convention as AA (14500) and AAA (10440) batteries, just larger. The 18650 format became the standard for high-drain portable electronics because it delivers significantly more capacity than AA lithium cells at the same voltage, and it's rechargeable with hundreds of cycles rather than single-use. Most tactical flashlights and stun batons that advertise rechargeable capability use either a built-in 18650 cell or an external slot for one or two 18650 batteries. When a device specifies 18650, any 18650 lithium-ion cell of the appropriate terminal type — button top for most stun batons and flashlights — is compatible.

How many times can an 18650 battery be recharged?

The UltraFire 18650 is rated for 500 charge cycles with 90% of initial capacity retained at 400 cycles. In practical terms, if you charge a stun baton or flashlight once a week, the battery will last approximately 9–10 years before capacity noticeably degrades. Daily charging shortens that to 1–2 years. The PCB protection extends usable life by preventing the deep discharge cycles that accelerate lithium-ion degradation — a battery that never goes below 2.5V retains capacity longer than one that's regularly run to complete depletion. When capacity does degrade noticeably — the device runs for significantly less time on a full charge — replacing the battery restores full performance without replacing the device.