The battery power rating on a flashlight determines how long the battery will last and how bright it is. The higher the number, the brighter it will be and the longer it will run.
Most battery ratings are measured in milliamp-hours (mAh), with higher mAh meaning stronger power and longer run time.
For example, a 1000mAh battery will last twice as long as a 500mAh one, while also providing more light output. It is important to bear in mind that higher mAh batteries are usually bigger and heavier, so they may not be ideal if you plan to carry your flashlight around with you.
It is also worth noting that some manufacturers may list the battery life as "hours" rather than mAh, so make sure to check the rating before making a purchase. In addition to battery power ratings, it is important to also consider lumens and lux when deciding on a flashlight.
Lumens measure the amount of light that is emitted by the source, while lux measures how bright an area will be when illuminated with a given number of lumens. Both are important to understand to get the most out of your flashlight.