I got in some 17340 LiFePO4 batteries from FastTech (HERE not an affiliated link). I charged them on a Nitecore D4 I just got and loaded one up. They fit first of all, and there is not enough room for an 18350 it would seem, but a 17340 is skinny enough. The LiFePO4 is the 3.2V “lithium ion” battery type (not 3.7V like the “normal” LiIon). I went with these as it seems they are a bit better for lower discharges not hurting the chemistry like it does a standard 3.7V LiIon. As this is an unregulated resistor circuit and will suck the battery down until it dies (~2V or so…) I figured this LiFePO4 type chemistry would be better for a light like this. The caveat, you have to have a charger that can SPECIFICALLY charge LiFePO4 batteries (Such as my Nitecore D4).
I ran the previous 16340 unprotected batteries for over an hour, but the light was warmer than I was comfortable with to continue. It was not burning hot, but for an area light that may be hanging somewhere in a tent or what not, too hot not to react if your head touched it. While a jumping reaction is funny in the sitcoms, knocking yourself and your tent partner out with the coconut sound of your melons colliding is not… Worst case scenario, yes, but still not why you want this little light.
The run time on the LiIon 3.7V was more than likely as long as Mhalen showed in his video on this light. I did not have a protected 16340 and so did not want to run it to lights out…
The run time test on the LiFePO4 3.2V is still on going as I write. The light got warm, but not really that far above room temperature, perhaps 90-95F. Great light output for the first three hours, greater than the 3V CR123 disposable battery. It will not have the run time of the disposable though. It is only rated at 350mah compared to the 1500mah of the CR123 disposable.
I used a singe 3V CR123 disposable, that was over a year past its “use by” date, for the four day weekend on July 4th. I was camping and used the light the entire weekend for miscellaneous tasks, and as a “candle” for a few hours each night. Dimmer by the end of the weekend, but still plenty of light.
While I will finish this run time experiment tomorrow for the LiFePO4, to me the winner for use in this light is already clear: The disposable 3V Lithium Primary CR123 battery. You have no worries with the disposable battery, they will last OVER ten years in a glove box or other place and still give you light. No chargers (special ones in the case of the LiFePO4) needed. Even retail you will be buying perhaps $5 worth of batteries every couple of years of intermittent use in a purse, glovebox or backpack.
If you plan to use this light frequently, and you have a LiFePO4 charger, get some 17340’s and enjoy the light. 16340 protected are too long (per Mhalen) and the 16340 un protected get pretty warm and you could damage the battery from over discharging it.
My opinion on a nice little light, thanks for reading!