Malkoff MD4/M91, want to run 3 Li-ion cells

Using a Malkoff MD4 host, will either the Surefire A19 or A14 extender allow the use of a 3rd li-ion cell? If so what size? Keeping in mind that the A19 or A14 would be stock, not bored.

I want to run 3 li-ion cells in an MD4 but don't know what extension I would need to do so or what size cells I would need.

This is not possible. The one thing you can do is run 3 18350's and a spacer but this will yield far less output than just running 2x18650's. And you are pushing the voltage maximums. Also, if you have an A19 that is not bored you don't want to put it on a Malkoff host. The Malkoff host is bored and you don't want to 17670s in a bored host. Rattling and less capacity. Even running 3x17670's will only get you 3*1600MAH, 4800MAH, compared to 2x18650s at 2900MAH or 5800MAH. But, this configuration wouldn't fit anyways.

Li-Ion's tell us their dimensions in their name. An 18 65 0 is 18mm in diameter and 65mm long. An 18500 is 18mm in diameter and 50mm long. A 17670 is 17mm in diameter and 67mm long, and so on. **Of note is that everything is give or take a few mm's. The springs in the tailcap make these adjustments for us.


CR123's are about 32.5mm.

An MD2 runs 1x18650 or 2xCR123's
An MD3 runs 2x18500 or 3xCR123's
An MD4 runs 2x18650 or 4xCR123's

I have an MD3 that I run with a bored A19 running an M91W. This simply makes it into an MD4. A19's are 1 CR123 cell extenders. I run 2xAW 2900MAH Protected Cell 18650 batteries.

Seen a different way...
MD2=65mm
MD2+A19=~100mm
MD3=100mm
MD3+A19=~130mm
MD4=130mm
MD4+A19=~160-165mm

The problem here is that the only possible combination would be 3x18500 cells. This results in the batteries not reaching the tailcap and there being space. Also, 18500's only have 1500MAH. 3 of them would still only add up to 4500MAH.

You are making too much out of this. So, no, in the long run it is impossible to run an MD4+A19 and any kind of battery configuration.

Simply buy 2 AW2900 Protected Li-Ion cells. Also get a Hi/Lo ring. They are 25 bucks. If you are concerned about run time you will be able to run the thing on low in this setup for an extremely long time.

The reason I am advising the AW2900's is because I have them and they work. I also have 2 Callies Custom 3100MAH batteries which use the Panasonic 3100MAH cell. Redilast uses these also. My Callie's however do not fit comfortably into my MD3 body. Therefore I would not recommend them for this application. I use them in an O-Light SR-51 and they are great, so the batteries are good, just a little bulgey for the Malkoff. They also fit in a Solarforce L2T that I have just fine. I think all Panasonic 3100 batteries might all be the same, slightly larger diameter, but I cannot confirm this.

Hope this helps.

You need a 68mm extension to run 3x18650's. There's an FM 68mm for sale over in the MP.

Is the 12 volt max rating for the M91 safe here though? I know they go to 4.2 then run at 3.7 'under sag' but is this dangerous?

I got an M91 recently & while thinking about it I read the M91 thread on here, someone asked the same thing & Gene himself said that it was perfectly safe running on 3 rechargeables.