Its actually milliamp per hour, not just milliamp.

https://en.wikipedia.org/wiki/Ampere_hour

Just like your home electricity is kiloWatt/hour(s).



You could have a 2 AA battery pack with a 2000mAh rating or a lithium Ion Battery pack with with a 2000mAh rating.

You can have LEDs which are more efficient than others and give more lumens of light per mAh consumed.

You can have different lenses and reflectors that make the beam wider or more focuses as well.

So, unfortunately, there is not a direct answer as to which battery technology will have longer output unless you eliminate other variables, i.e. have the same light with adapters for different technologies.

You'll find that different technologies might be able to provide more energy compared to their weight https://en.wikipedia.org/wiki/Rechargeable_battery#Types but what often happens is electronics utilizing a battery type with a more efficient power to weight ratio are often use physically smaller cells so you get a similar amount of runtime from both. Think how a smaller car might be more efficient mpg wise but have a smaller tank and a larger car, while getting less mpg, will usually have a larger tank so they can both typically drive the same distance before needing a fill up.

I used to standardize on AA powered devices, be it lights or GPS or camera, and a carried a pack of spare AA's. However I've begun to transition to USB rechargeable devices, not only for the smaller size and weight, but also the ability to have them all connected via the smallest/lightest USB cables I can find, and keeping those devices always connected via those cables to a battery bank in my backpack. Could that be an option for you as well? Do you carry/wear a backpack on outings?