1 vs 2 18650 cells

Two questions involving this scenario:

1) Should we expect noticeably more output with two cells if the flashlight is optimized for it? I know run time will be longer but I've always been curious if two 18650's will actually give me noticeably more output if the driver accepts that much voltage. I guess I don't understand why it would get brighter if the emitters cap at a certain amount.

2) What risks are inherent while running two protected cells? I understand maintaining similar voltage from both cells but what's going to happen when something does go wrong? I've have only ever run one protected 18650 and never contemplated the risks from running two. And I will always run protected cells.


I understand how this is beneficial to the triple XM-L lights but will it provide an increase in output for the single emitter lights?

A two cell light 75% of the time wont put out as much lumen's as a single cell. If optimized to push 3A to the emitter then yes it will have as many lumen's.

Most are not optimized due to the costs involved and also drivers many times are aimed at long run times over high lumen's. This is why you will see a light with 2 cells fully charged put out almost half the amps when first turned on and right before the cells cutoff at 3v it will double. It will start at 1.5A at the emitter and end at 3.5A's many times. This gives the most run time and the brightest light even as the cells die off.

The only reason in 95% of the cases you should buy a 2 cell light is for long run times, It never leads to a brighter light at least not until the cells are about to cutout.

BUT, For instance there are lights made for max lumens with 2x and 3x 18650's like the Sky Ray 3800 and its driver pushes the 3 emitters at the same high amps the whole time it is run iirc on the drivers stats.

BUT #2 a two cell light can fool your eyes with the look of more lumen's as it has room for much larger reflectors in diameter and depth.

As long as you run protected cells that are very closely matched in voltage you will have very low percentage of issues unless the protection fails, But many times the lights protection can kick in and catch it also. Ive run unprotected cells in two cell lights and made sure the lights protection is as good as possible and had no issues, But its just a matter of time before i get bitten also. Always double check you don't reverse the polarity by not paying attention, But most cases the light will catch that. And if you suspect a cell is not holding a charge and its capacity has dropped alot that is a cell that could put the other cell in a runaway situation but hopefully the cells protection catches it.

Generally multi emitter lights with dual cells will push more lumens and amps as thats what the light is designed for which is extra lumen's. But thats not always the case and you should look for a lights review before buying if possible, And being the Guinea-pig for a new light is usually less rewarding than a home run.

Ive looked into building 2 cell lights with a single emitter and to do it the driver with good regulation that keeps the emitter at its peak amps at all times are usually so expensive they take up half the cost of the whole build making building your own two cell light not such a smart move many times. And if you gonna use XML emitters you usually have to steal drivers from the SST-50/90 line as it seems driver makers still arent interested in 2 cell XML drivers yet.

A lot of great information there. Since I'm researching for gifts (I have more and more people approaching me to get them 18650 flashlights after seeing mine) I would prefer to stay on the safer side. It seems a single 18650 is most suitable and then just have charged cells for backup. Unless, of course, I'm going the triple XM-L route then I'd be fine with multiple cells. Personally, I'm always good with just one cell for a regularly used light because I only need it in short bursts and I'll have a charged cell waiting just in case.

The KiaDomain C8 XML 3 or 5 mode light is $25 and about the best single 18650 light for the money. Since it doesn't use a P60 drop in like most budget lights do it throws much better and has more spill even tho its lumen's may be on par of a P60 drop-in light.

Its actually driven so well that you have to reduce it to medium at times so it cools down some as it will overheat to the point you cant hold it, Unless you live at the North Pole.

There are several 2 cell lights that get high ratings in the 18650 light section that do work decently, But the 3 led Sky Ray 3800 rev2 is the best bet for the money in dual cell lights. ManaFont.com has that and and i think they only sell the rev2 now only. Its a beast no doubt At $50

The benefit of a 2 cell light w/ xml's is that it's necessarily regulated to some degree, whereas almost none of the 1 cell ones are. However 2 cells come with the inherent risks of running multi-cell which is probably not the greatest idea for a gift to someone who isn't going to mind the state of them. Basically if you try to use a full & empty battery (or perhaps insert them wrong) the result is potentially catastrophic (ie pipe bomb).

If you're going to gift a xml light, I can recommend the Xtar R01. It's a well built light w/ built-in charger. Xtar sells them direct for ~$40, and worth price difference to the cheapo lights. Just do a search for it.