Thanks guys, I'll try out their warranty service as suggested. I did try changing the battery too, but no go. The problem probably lies with the electronics if it isn't the LED.
I still remember throwing my Arc LSH-P whilst lit on a carpeted floor so hard it bounced back up, just because I knew it was tough enough. My Arc AAA was from a time long gone by, back when the HD Luxeon I and the NX-05 optic were hot stuff in the LED arena, and Peter Gransee was a CPF regular. It was one of the models with the lengthwise inscriptions on the knurling, made during Arc's legal troubles with Mag Instruments that precipitated the company's eventual demise.
I remember being overjoyed when I received it, having won the HA tint lottery along with the added bonus of having a warm-tinted Nichia LED in a non-premium model. It lived a fruitful three years, travelling with me around the world to Malaysia, Thailand, Italy, France, Germany, Switzerland, Luxembourg, Belgium, the UK, and the Czech Republic. It found keyholes and lit the way to the bathroom at night countless times, and it did an excellent job of wearing out my keys. Here it is, used and rough around the edges, though never abused:
Let's observe a quiet moment for the little guy