Nitecore MH20 in neutral white stop working in less than 2 months

My Nitecore MH20 in neutral white have stopped working in less than 2 months.

Is there a lock out function that I do not know?

Read in the manual that the lock out function is loosen the head so that there will be no battery contact.
However, the head is tighten all the way.

I have used the Nitecore 18650 3400 mAh lithium battery for this flashlight.

Any quick fix?

There is no lock-out function other than the slightly lossening the head. Might want to check the contacts, etc.

Not trying to be facetious, but have you tried another cell?

before you return it do the standard protocol of taking a q-tip and some rubbing alcohol and go over all the lights contact points then yes try a different cell. If that doesnt work send it back

I was sure I had the very same issue. But...

My MH20 had been 'on the shelf' for maybe 10 months, when I recently wanted to put it back in service. Instead of using the micro-USB interface on the MH20 itself, I simply unscrewed the rear cap and popped the 18650 (NL1826 Nitecore 2600 mAH cell) into my Opus-C3400 to charge: I wanted to test the capacity of the Nitecore 2600 mAH battery supplied with it - as well as the two Nitecore NL189 3400 mAH cells supplied with the kit I bought from Amazon back in October 2016 - now seven years ago. (The C3400 charger / tester charges / discharges / then charges each of four cells completely independently. It also does < not-sure-how-reliable > Internal Resistance measurements.) Surprisingly, after seven years, these cells are holding up remarkably well: the two 3400 mAH cells measured 3294 and 3305 mAH, while the 2600 NL1826 cell measured 2633 mAH - actually higher than its rated capacity. IRs were still good, with all three cells measuring around 100 milliOhms based on multiple trials (trying to pay attention to minimizing contact resistance - to get consistent results). Not quite as good as some of my newer Samsung 25R / 30Q cells (which measured more like 50 milliOhms; but still very respectable for their age ...)

I digress. After topping up all three 18650s I put the original cell back in, screwed on the back cap again tightly - and pressed the on / off switch. That's odd. No blue lights from the switch button to tell me the voltage. Not a glimmer. Nada. Nothing. I kept clicking: zippo. I unscrewed the back cap and tried one of the other cells. Same non-result. I couldn't believe it; this light has always been super reliable and had never failed me.

I went to the internet, looked at videos. No joy. I came to this Candlepower forum. Sounded like my MH20 may have died?

I printed out the manual and read through it thoroughly...

Duh!*! The text reminds the user: "As a matter of good practice, when putting the unit away for an extended period, unscrew the HEAD a turn or so to ensure it CANNOT turn on while in storage."

HEAD? What about the head? There's yet another place to open the flashlight? Oh wait - that's right. In the intervening months since I'd put it away, I had forgotten that design detail.

But evidently - back early this year when I put it away - I had dutifully done just that.

Returning to the unit, I grasped the head. It did not seem loose, but I gave it a firm twist and Lo - it turned.

Problem solved. I felt like a fool - but returning to this thread, I wondered if that might be another possibility for one to try if experiencing this issue. So...

Talk about a long-winded way to get to the point - but hope it may be of some value to another MH20 owner.