How does installing battery backwards damage a torch?
Without knowing the schematic of the flashlight (torch), it's hard to say. Some might have reverse voltage protection, some might not. Since it states it outright, it probably does not. Since some of these high performance ones have integrated ICs for boosting the battery voltage from 3v (CR123) to the needed operating voltage of the (assumption) LEDs and control circuitry, reversing the voltage can cause a breakdown of sensitive parts.

There are three main sets of circuits that these advance flashlights can have.


LED Driver (Boosts power from low voltage battery to LEDs)
LED Control (Microcontroller in the Switch allowing various dimming levels or features like signal flashing or patterns)
Battery Charging (What it says on the Tin)


If any of these lack reverse voltage protection, they can break. And that specific one has a temperature sensor. Don't know why, probably for thermal shutdown reasons.

On the other hand, my dollar store 9 led flashlight has exactly three parts to it. 3 AAA batteries, 9 LEDs, and a simple Switch. No resistor, no current control. It depends on the resistance of the batteries, the high current load of 9 LEDs in parallel, and they often blow leds over time. Very simple, and while a practical design for it's intended use and production cost (pennies on the dollar), NOT performance oriented.

Essentially, you are underestimating the complexity of the flashlight in question, and overestimating your simple electronics knowledge.