PSA: This is why you should avoid Ultrafire and sketchy Chinese batteries. There's no protection circuit, despite their claim, and their advertised capacity is 9 times what they're capable of. : r/flashlight
Test of UltraFire BRC18650 3000mAh (Red-silver)
UltraFire 3400mAh 3.7V 18650 USB Rechargeable Lithium Battery with Pro
UltraFire 18650 Lithium SS-0340 Array
UltraFire 1800mAh 3.7V 18650 Li-ion Rechargeable Battery Without Prote