How safe is a single 18650 flashlights

I value safety when using my lights and I only buy single 18650 lights powered by protected batteries due to this.
How safe is it if I do not test my batteries and simply charge and use. The charger I use is Tustfire TR002 Lithium battery charger.

Batteries I use consist of protected AW, solarforce, ultrafire gray and xtar.

Is there a posibility of explosion?


I use the same charger among others. Do you run the light until it stops or charge after a period of use? Buy a Dmm and test if you are worried.

Sometimes I use the light until its dead and until a noticeable drop in output. The reason I use only protected batteries.

You will shorten the lifetime of your batteries doing that. I charge mine at around 3.8 or higher

Its as safe as you are - Thats the bottom line ..

The greater the charge to discharge level , the faster cells deteriorate .. Ie ... If you consistently discharge to 3v the cells will deteriorate much faster than if say you discharge to 3.5v

Usual things to watch out for , cell quality / condition , shorts , damage , overcharging - over discharging ...

Realized that, so if I charge them at a slight decline of output will this enough to preserve the batteries?

Has anyone encountered problems like explosion from a protected batteries in a single flashlight format? I'm more concerned in explosion specially during use under critical circumstances.

Perfect advice. An explosion would be extremely rare if you follow this. You will need to get a DMM to test voltage.

My understanding is that the most common cause of cylindrical lithium failures is from reverse charging in multicell systems. This is why I only run single cell lights.

I don't particularly agree with this "only discharge to 3.5 volt" sentiment as you are not using the full capacity of the cell. As long as you don't discharge the cell below manufacturers rated specification, you should be fine.

On charging, I don't know about that TrustFire charger but I have had bad experiences with UF chargers overcharging my cells. I spent the extra money on a 4Sevens charger that follows the correct CC/CV charging method. I mean, it is only about 25 bucks.

Though double 18650 lights are fun.

Hmmm , I think I understand the question , what flashlight - current draw - is it well regulated ...

The easiest thing is to get a Multi Meter , the cheapest one will do as your measuring voltage ... Most aim to charge 3.5v to 3.8v range

If you have a well regulated light , by the time you notice dimming it may be down bellow 3.5v [ its not critical - you can buy more cells ] If you look after cells they may last 3 year or more , if you abuse them they may be good for 1 to 2 years .. By then there should be some improved cells in anyway ...

Now the second part , critical circumstances ???????

Ok , this would depend on flashlight design , as well as how well the light is set up ... And the circumstances that are critical ...

But definitely you may need to set up the light if its going to suffer harsh treatment .

Thanks for the advise old4570, I actually just bought a multi meter but having trouble using it as my left hand is in a cast.

I've been using my batteries on solarforce lights, RQ and now the Trustfire X9.

I actually only use 18650 lights occasionally if I need a powerful light for spotting things and as a bright light for camping/hiking. I normally use my AA powered lights as edc and for most of my needs.

My concern is if I abuse the use of my batteries, will it cause any other negative impact other than shortening its life? Critical circumstances is during a camping or night climb, don't want to have explosion during a climb.

I just learned to use the multi meter and here's the voltage of my batteries before usage. is this good?

Charged few days ago

AW18650 - 4.22v

AW14500 - 4.21v


Ultrafire gray - 4.08v

Months in storage

Solarforce18650 - 4.16v

Trustfire flame 14500 -3.74v

trustfire gray 10440 - 3.66v

they are all within voltage. i think under 3-3.2v is need to worry

Thanks for the info,

Just a question, As I use a battery during a climb and drained it until the protection circuit kicks in, is it safe against any explosion or venting? I only use protected batteries.

protection usually blocks over discharge, so yes. but it can reduce the cells life.

Thanks Pulsar,

I'm waiting for my XTAR batteries to use in the X9, love my bright lights but hate the risk so making sure what I use is as safe as possible.

As long as it is so dangerous to use and recharge lith ion batteries ordinary users will be scared away.

And yet..........

All of us use lith ion batteries every day in laptops and cell phones.

Why can we put a lith ion up to our ear and be safe, or put our fingers up to a laptop and feel OK, and yet.....if we use them in a flashlight we suddenly need to feel fear?

A little off topic but does the X9 have anny PWM on the low/medium modes?


All of the 18650 cells I am currently using are salvaged from laptop battery packs. I do desktop support and many of my users frequently drain their laptops down until the laptop goes to standby or keeps their charged to maximum continually. I have never seen a battery explode. I try to use common sense when charging and never run a light flat, but am not extremely worried about explosive failure.

I try to abide by the following chart when using li-ions in med to high draw lights:

4.2V – 100%
4.1V – 87%
4.0V – 75%
3.9V – 55%
3.8V – 30%
3.5V – 0%

So running it only to 3.8-3.7v is fine. Why risk over discharging when we probably have a few extra cells to use anyway? Just pop in another fresh cell.

I ran a fresh cell (4.17v) in my X9 for just 10 min...1 min at a time with 10-20 sec of rest in between. I took a reading and it was already at 3.97v.

And yes the X9 has PWM in the lower modes.