Yes, fraid so.
Your best bet though is to use a Protected 18650 which gives you an extra layer of security. Id trust the battery circuit moreso than flashlight electronics, especially a cheapo.
The cheapest 18650 you can get is 30 bucks at DX for a P7. Those won't have any protection.
Yeah, itp C6 is a good choice. Its input voltage is 3.0 to 6.something. This means that once the 18650 drops below 3, the light should cut off anyways, even after the low voltage warning.
By 2.6 (the danger level) the light should be off. I'd still get a protected battery, but I think this is about as cheap as it gets.
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Is there a reason you want an 18650 light? Do you already have protected 18650 batteries and charger?
I mean, looking at the C6, it doesnt seem to be any better than a 2xRCR123 light such as the itp SC x2, which has MORE brightness, will be more efficient (sligltly), and has infinite bright adjustment for 39.99! (minus discount)
In general, the only reason to go with an 18650 light is because it cranks out 700 lumens. (SST-50, P7 or MC-E light). I am not seeing any real budget choices that do so, so I'd just use 2xRCR123 lights instead. Or you can do with rechargable AA lights as at least the AA/AAAs are useful for other home electronics.
If you are really wanting a big bright light, then that is a different discussion.