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_{Using a single Cree XP-G driven at 1000 mA (250% luminous flux; about 300 raw lumens), you are burning 3.2 volts × 1 A = 3.2 watts. A high quality 18650 is 3.6 A × 3.7 v = 13.3 watts. Boost driver efficiency at 85% gives you 11.3 watts, so you have just under 4 hours of time with an 18650 at full (250%) power.}

_{Mountain bikes have a handlebar diameter of 22mm  . 18650s have a nominal diameter of 18mm (i.e., 18-650) but are often closer to 19mm actual because of the insulation and power protection circuitry). It's a tight squeeze. It won't work with many drops.}

_{Using a single Cree XP-G driven at 1000 mA (250% luminous flux; about 300 raw lumens), you are burning 3.2 volts × 1 A = 3.2 watts. A high quality 18650 is 3.6 Ah × 3.7 v = 13.3 watt-hours. Boost driver efficiency at 85% gives you 11.3 watt-hours, so you have just under 4 hours of time with an 18650 at full (250%) power.}

_{Mountain bikes have a handlebar diameter of 22mm. 18650s have a nominal diameter of 18mm (i.e., 18-650) but are often closer to 19mm actual because of the insulation and power protection circuitry). It's a tight squeeze. It won't work with many drops.}

_{14500 lithiums would fit for sure as they're the same dimension as AAs (14mm D x 50mm L). However, they only have 900 mAh (fake ones will advertise more but are fake) which is 3.2 watt-hours or about 3 watt-hours after booster. So just about one hour of full (250%) power with one 14500, but you can serially gang the 14500 into two or three, depending on the curve of your handlebar (which would limit which bars it could fit into).}

_{Using a single Cree XP-G driven at 1000 mAh (250% luminous flux; about 300 raw lumens), you are burning 3.2 volts @ 1 Ah = 3.2 watts per hour. A high quality 18650 is 3.6 Ah @ 3.7 v = 13.3 watts. Boost driver efficiency at 85% gives you 11.3 watts, so you have just under 4 hours of time with an 18650 at full (250%) power.}

_{Using a single Cree XP-G driven at 1000 mA (250% luminous flux; about 300 raw lumens), you are burning 3.2 volts × 1 A = 3.2 watts. A high quality 18650 is 3.6 A × 3.7 v = 13.3 watts. Boost driver efficiency at 85% gives you 11.3 watts, so you have just under 4 hours of time with an 18650 at full (250%) power.}

• If you're using inexpensive and low-power 5050 LEDs, then you can power the lights off button cells but really don't have enough lumens to be compelling against $5-10 strap on lights.

• If you're using high power Cree type LEDs (3.2 watts/300 lumens), you can charge more but you are going to run into problems with battery life, installation, charging, and optics with your design.

• If you're using inexpensive and low-power 5050 LEDs (15 lumens@350mW; usually ganged in groups), then you could power the lights off button cells (two CR2032s would power one 5050 LED for about 3 hours; 3 x 5050s for one hour) but even ganged you really don't have enough lumens to be compelling against $5-10 strap on lights.

• If you're using high power Cree type LEDs (300 lumens@3.2 watts), you can charge more but you are going to run into problems with battery life, installation, charging, and optics with your design.