Electrical calculations for batteries?

- what's the voltage and type of the battery?

If I had to take a wild guess, the battery is a chinese 18650 Lithium battery, since these are the most common for flashlights with a single battery.

Also, if the flashlight only has a single battery, it most likely will only have a single LED (again, guessing that it's an LED flashlight).

In this case, both the '7W' and the '4500 mAh' are bogus. In real life, that's probably more on the order of 3 Watts and 2500 mAh, but then again, the ratio between those numbers stays about the same.

Now, at 3.6 Volts and 2500 mAh, that battery holds 3.6 * 2.5 = 9 Wh, so at three Watts, the battery will be good for three hours. Deduct a little bit for the higher discharge current, but you should be good for about 2.5 hours.

Specs are often exaggerated, and run time depends on the battery voltage. Charge battery fully, switch on torch and time it.

Run time can be crudely calculated. If it's a 3.6V battery it will deliver 2 amps for a 7 watt load, so my guess is 1 to 2 hours. There may be a lower power setting on the torch which will give a longer run time.

The capacity of a battery is usually based on an average current which will flatten the battery in 20 hours, and your run time will be much less than 20 hrs, so the battery capacity will be reduced. Really the only sure way to find the run time is to try it out and see.

Theory is one thing; practical use is another.

I've never seen a situation in which actual battery life

was even close to the results of calculations.

The best way to know how long you can use a light

on a set of cells is to time it as you use it.

Each new set of cells will usually last for a period of time

either longer or shorter than that of the preceding set.