Surefire Mods for 18650: Fury, U2, & Kroma???

I just bought a Nitecore charger and four of their 18650 rechargeables for my newly-acquired Olight S2-CU Baton on Malkoff MD2 (M61W & retaining ring high/low switch). Now I'm interested in modifying a few of my other lights for the 18650 battery. I'm definitely having my Surefire C2 Centurian HA with Malkoff M60 done, likely by Precision Works. It has my first nice light and I bought it early in my military career so it's special to me. I think it will see more use after the conversion.


I'm also interested having my Surefire Fury, Kroma, and U2 done but I don't know if their electronics would be compatible with the 18650. I have no knowledge about such things but I'm sure someone here does. If they would be compatible I'll ask Precision Works about doing the machining on those bodies.


By the way, I really like the S2-CU and Malkoff. They are both excellent lights. The M61W tint is so nice and the copper S2 is beautiful with many great features. These Lumintop Tools are seeing a lot of use too. Great little lights. The beam shot photo was done with my iPhone. White balance is not perfectly adjusted but look at beautiful incandescent-like color of the Malkoff M61W. It is very pleasing.

Hm, nothing.
Well I called Malkoff today to talk about batteries. They are super helpful. I talked to Gene last week about the MD2 I bought. Today I talked to Tony (I think that was it) who recommended skipping the boring for 18650 on the C2 and just using 16650s. So I picked up an M361N for the C2, a clicky switch, and a few 16650s. I think I've got a Surefire 6P stashed somewhere. I'll probably just throw the M60 in there and keep it in the truck with primaries.

I also called First Light about 16650s in my Tomahawks (GP, NV, and 2 MCs). They are also some nice folks and said the 16650s should work in the Tomahawks. These are my most used lights because they are great for dog walking. My wife won't use anything else since I put one in her hand. I realized that the Tomahawks really cover all the capabilities of the Kroma and U2. With the MD2, upgraded C2, and other lights I've picked up I'll probably just sell the Kroma and U2. I just never reach for them any more. Maybe the Fury too.

If you can remove the head from your SF Fury, Fivemega has a body that's already bored for 18650's. That way you don't have to mess w/ the stock body. Also, the Fury works great w/ an 18650.

I have run almost all my SF's on 17670's without mods for many years. I do now run my Fury on a Fivemega body but the 17670's worked great.

I bored my Fury using the drill bit and sandpaper method and it runs fine on a 18650 battery.

I ended up buying some 16650s to try.
Here is what I'm doing with various lights now:

• First-Light Tomahawks: I have several of these and two of them are used daily for dog walking so I am using the 16650s in those. The lights seem to run fine with them aside from one issue. The maximum white light setting will run at max brightness for just a second then step down to about 75% brightness (a total guess but no way to really measure it). For the given purpose I'm fine with that. I'll be happy to loose some max brightness and save money on the batteries. The max white still brighter than the mid white setting. I haven't noticed any difference in functionally on the mid/low white settings or colored LED settings. I've only been using the 16650 for a few days so it will be interesting to see how long the max white setting functions before it needs a recharge.
• Surefire U2 & Kroma: I am going to keep primaries in these. The Kroma is in a bug-out bag of sorts and the U2 is my "bump in the night" bedside light. I think primaries are better for those roles.
• Surefire Fury: I forgot about it in the safe. I'll have to try the 16650s in it tonight but it doesn't have an active role right now.
• Malkoff MD2 w/ Hi/Lo Bezel Switch and M61W: Awesome light. Awesome. This one rotates for use around the house and sometimes in my EDC bag. I use 18650s in it.
• Surefire C2 Centurian w/ Malkoff Clicky Switch and M361N: Another awesome light. I use 16650s in it as Malkoff recommends for this emitter. This one rotates for use around the house and sometimes in my EDC bag.
• Surefire 6P w/ Older Malkoff M60: This one will likely end up being my truck/motorcycle light so it will use primaries. It's just an older, kind of beaten-up body I had lying around so I decided to throw the M60 in it after upgrading the C2 to the M361N. I also ordered a Malkoff clicky switch and pocket clip that should arrive in a few days. I will keep primaries in it.
• Olight Baton S2-CU: This is a great little light that is always in a sheath on my EDC bag. It uses an 18650.
• Lumintop Tool Titanium, Nichia 219B LED: A great EDC light that is always in a sheath on my belt with a small Swiss Army Knife. I keep a rechargeable AAA in it.
• Lumintop Tool Copper, Cree XP-G2 LED: Another great EDC light that I keep in the case that holds my passport and a few pens. I keep a rechargeable AAA in it.
• Surefire EB1/L1/E1L & Novatac 120P: These are lights I picked up for good prices on some forum classifieds. I keep them around for various stuff like looking through the gun safes, range bag use, and sometimes carrying in a pocket. I've thought about trying rechargeables in the Surefires but they don't really see enough use to justify it.

I tried a 16650 in my Fury tonight and it seemed to function fine. So as far as functional differences between a 18650 and 16650, I think I'm just looking at longer run times with the 18650, or am I mistaken? I'd rather stick to the 16650s than modify for 18650s.

A few photos of some of my lights. I'll take some more after my other parts arrive from Malkoff.

One more thing to point out, there are rechargeable batteries in the same size as the primaries CR123A.

They have LiFePO4 chemistry and produce the same 3.0 voltage nominal (so lower than the Li-Ions).

You can use these the way you would use primaries, so if your Surefire uses 2xCR123A primaries, you'd just pop in 2xLiFePO4's instead and be good to go.

Main disadvantage: lower capacity. Also, you'd need a recharger that can deal with it, the standard Li-Ion charger, unless it has a special setting, cannot be used.

Other advantages: high discharge rate, excellent recharging potential (usually at 2,000 cycles), quite light in weight, much lighter than NiMH for example. Plus, they are considered safer to use than the Li-Ions.