Flashlight is applicable to function under outdoor work, mine, railway, power maintenance. In future, this product will be widely used. As an important parameter of flashlight, brightness reflects light bulb range and is determined by battery current and voltage. Thus to a flashlight, a matching lithium battery is vital.
Following illustration is based on 16340 battery used on 7.2V/0.85A flashlight.
There are many types of lithium battery used on flashlight, among which, 18650, 17670, 16340, etc are common. First we should understand their meaning. The first two numbers in front of battery model refer to battery diameter and three numbers behind means height. Take the 18650 battery for example. Diameter is 18mm and height 65mm.
Rated voltage and discharge current on flashlight bulb require lithium battery no over current and over voltage. For 0.85A bulb, best discharge current is 0.85A. If current is small, flashlight will not be bright enough. On the contrary, over current might damage battery structure. Thus best-matching battery could not only obtain greatest brightness but also avoid damaging battery.
7.2V bulb should be powered by two lithium batteries in serial. This is because rated voltage of lithium battery is 3.6V-3.7V and voltage of two 3.6V batteries in serial equals 7.2V. on the other hand, if voltage of lithium batteries in serial is far higher than bulb voltage, over voltage work happens, which will cause light bulb burned. Thus if a flashlight previously uses Ni-MH battery, it should change bulb in case it requires to use a lithium battery. over voltage can make flashlight brighter but could burn bulb.
Lastly, for flashlight lithium battery charge, lithium battery charger determines whether battery is fully charged according to voltage value. Cutoff voltage of single lithium battery charge is 4.2V. Original charger will automatically charge to 4.2V and stop charging.