First off is the light on at the back of the light when the battery is connected.?

Nope, died along with the main light. To add another problem, my multimeter is in my car, which isn't here... Balls.

One of two things I think. Battery fault or battery dead. Is it still dead after a bit of a charge?

The chargers can spaff up too. One of mine did. If you know anyone with another battery you could try that. Replacement chargers are availible from DX.

They will cut out. Usually drop to low power, then shut down to prevent over-discharge damage to the battery.

It could be a faulty switch or a faulty battery pack. The battery packs wiring is a 'weak point'. Trout (I think) on here sells decent replacement packs that work reliably.

On mine the switch turns red (from green) when the power starts to drop off. But when the power runs out it, unsuprisingly, turns off. What else do you expect it to do when the battery runs out?

Smudge is the person you need on here

Works after a quick sesh on the charger. I might buy a spare batt to have with me - got loads of dirty looks riding home on the pavement sans front light!

I had it on strobe and didn't notice a drop in power before it went off, first time I've ridden it in actual darkness though so maybe it just seemed bright.

Cheers the replies guys.

Edit: is smudge the mtbbatteries guy?

I might buy a spare batt to have with me

Charge it daily.?

I've got a memory like a sieve, that's never gonna happen!

A similar thing just happened to my light tonight. I was cycling home and it started flickering then cut out, I was on a rough bit of tarmac. The light on the back of the light still glows, and if I wobble the light around it flickers on and off. Dodgy connection in the light?

I had this with mine last week. Took it apart and and it was the little coil thing (inducter?) that had come away from the board. Five minutes with a soldering iron and job done.

Cable entry points at flex protectors etc are also known weak points for random shorting out/disconnection.
I'd strongly recommend reinforcing all cable entry points with self amalgamating tape from new. (Wrap the battery pack in a thinn layer of it too whilst you're at it.)

I just bought a new one, tried to take it apart last night but couldnt. I'll have another go with some better tools, but that metal disc is screwed in too tight!

both my DX (Magicshine 900l & XML) cut out the other night at the end of a ride, no warning, from full power to out. Batteries were flat, recharged and they have been fine since. I had used both for 3.5 hours on full power, so I would think its normal.