Convoy has released a new 21700 cell light.  It’s a single emitter thrower style light.  Read on for some testing!

Official Specs and Features

Here’s a link to the banggood product page.


There’s only one body style of the M21B, but it’s available in 6500K and 5000K temperatures.  The 6500K is seen here.

Price and Coupon

This one is currently going for a reasonable $26.99.  That’s a referral link – clicking it won’t affect your price at all but will help me continue posting items like this one for review.

Short Review

This is a inexpensive and well made middle range thrower, which benefits from the extra capacity provided by 21700 cells.

Long Review

The Big Table

Convoy M21B
Emitter: Luminus SST-40 (6500K)
Price in USD at publication time: $26.99
Cell: 1×21700
Turbo Runtime High Runtime
LVP? Flash Warning
Switch Type: Mechanical
On-Board Charging? No
Claimed Lumens (lm) 2300
Measured Lumens (at 30s) 1806 (78.5% of claim)*
Claimed Throw (m)
Candela (Calculated) in cd (at 30s) 1308lux @ 5.634m = 41518cd
Throw (Calculated) (m) 407.5
All my Convoy reviews!
  • Measurement disclaimer:  I am an amateur flashlight reviewer.  I don’t have $10,000 or even $1,000 worth of testing equipment.  I test output and such in PVC tubes!!  Please consider claims within 10% of what I measure to be perfectly reasonable (accurate, even).

What’s Included

  • Convoy M21B Flashlight
  • Lanyard (already attached)

Package and Manual

Typical Convoy package.  Usually these get to me quite beat up.  But the contents don’t show any wear.

There is no manual included.

Build Quality and Disassembly

Build quality is exactly on par with other Convoy lights.  No better, no worse.  Considering that it’s only $27, it’s exceptionally well built.

The knurling is perfect.

The head has acceptable cooling and mass for the 5A 100% output.

The cell tube removes quite easily and has big beefy square cut thread on both ends.  The anodized threads means that the light can be mechanically locked out easily (even past the lockout that the mechanical switch provides).  The cell tube is reversible, too.

Both head and tail end have springs.

And both springs already have the spring bypass.

The bezel unscrews easily, and the aluminum reflector comes out, too.

This reveals the emitter, which has a nice big centering ring.  Swapping the emitter should be a breeze.

Size and Comps

Officially: Diameter (Head/Body) 35.7 / 27.1mm
Length 141.5mm
Weight 120g

It’s a fairly good handling light.  It could have more mass in the head, and/or a larger reflector and not suffer, but it’s good as-is.

Retention and Carry

There’s really only the lanyard for retaining the light.  There are holes in the tailcap for attachment, and the lanyard ships already installed.

Actually it ships installed a little incorrectly, since the better way would be to loop it through two holes instead of just one.  This would allow easier tailstanding.

There’s nothing else.  No pouch, and no pocket clip – it’s not really suited to clip carry though.

Power and Runtime

Primary power for the M21B is a single 21700.  With springs on both ends, any type 21700 should fit and work just fine.  The M21B will also work with other cells like 18650 or 20700, too.

You’ll likely want a fairly high quality cell, because the M21B draws around 5A on 100% output.  Here’s a runtime on 100%.  Basically the light starts at 100% and then tracks down just a little before settling out at around 1550 lumens.  After that output falls as cell voltage falls.  There isn’t LVP, but the main (ie only) emitter flashes to alert to low voltage at around 3V.  This flash is noticeable and quite dramatic because at this point the output can still be as high as 700 lumens.  So a flash from 700 lumens to off for a second is quite noticeable.

Output on the next lower level (30%) is pleasantly well regulated for just over two hours, at which point the low voltage warning beings.

Modes and Currents

Mode Mode Claimed Output (lm) Claimed Runtime Measured Lumens Tailcap Amps
100% 100% 1806 4.94
30% 30% 738 1.52
3% 3% 78 0.17
0.1% 0.1% ~ 0.03

Pulse Width Modulation

No PWM on any mode with this light.

For reference, here’s a baseline shot, with all the room lights off and almost nothing hitting the sensor.  And here’s the worst PWM light I have ever owned.  Also one of the very first lights I ordered directly from China!

User Interface and Operation

The switch is a very Convoy switch:  mechanical tailswitch – a reverse clicky.  It’s a big switch with some texture for grip, a fairly low action, and very clicky.

Neither the Convoy official page nor the BangGood page describe the UI of this light.  And with no manual, I’m kind of just free wheeling it.  That said, it’s probably mostly like other single switch Convoys – the T2 for example.  This does not seem to be Biscotti.

Here’s a UI table!

State Action Result
Off Click On (Mode Memory)
Off Half Press No Action
On Half Press Mode Advance (LMHT)
On Click Off

There does not seem to be any strobe (yay).  Also no shortcut to anything (boo).

LED and Beam

The emitter in my review copy is a 6500K Luminus SST-40.  Also available is a 5000K option.  The deep wide reflector is very smooth.

These beamshots are always with the following settings:  f8, ISO100, 0.3s shutter, and manual 5000K exposure.

Tint vs BLF-348 (Killzone 219b version)

I compare everything to the Killzone 219b BLF-348, because it’s inexpensive and has the best tint!

Random Comparisons and Competitive Options….

Here’s a link to a relevantly filtered page on  I use that site a lot!  There’s not much else comparing to the M21B at the moment.  Certainly nothing in it’s price class!


What I like

  • Build quality for low price
  • Throw is respectable

What I don’t like

  • No LVP
  • Would be nice if the UI was Biscotti, at least


  • This light was provided by BangGood for review. I was not paid to write this review.
  • This content originally appeared at  Please visit there for the best experience!
  • Whether or not I have a coupon for this light, I do have a bunch of coupons!!  Have a look at my spreadsheet for BangGood and GearBest coupons. Please subscribe and get notifications when the sheet is edited!!

11 thoughts on “Convoy M21B Flashlight Review”

  1. Pingback: Convoy S12 Flashlight Review – ZeroAir Reviews

  2. As far as I can see the M21B seems better than S12. It has a higher brightness and is a little bit cheaper. UI and build quality is the same.
    Do you agree with me or have I forgotten something?

    1. I don’t disagree but I think the lights are different enough that you might want one over the other. One’s a single/thrower and one’s a triple. I really wouldn’t compare these two in that way.

  3. Thanks for your answer. Another question, do you recommend protected or unprotected battery? Is 10A discharge current enough?

    1. Yeah, 10A rated should be enough. As long as whatever protected cell you use doesn’t trip at that current then you should be ok.

  4. No LVP? This theoretically has an identical driver to the S12. I wonder if convoy has variations on their 22mm driver now.

    1. Hi ZeroAir,
      I wanted to ask again, if you have an answer to this question, or how you come to this statement that M21b does not have LVP?

      1. As tested with the bench power supply I mention often. There’s definitely a LV warning, which I mentioned (and is visible in the runtimes, even).

    2. > No LVP?

      As tested with the bench power supply I mention often. There’s definitely a LV warning, which I mentioned (and is visible in the runtimes, even).

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