Advice Needed

Hi there. I'm new here and would like ask you flashlight experts for some advice to a problem I'm having.
I'm not too knowledgable in this area so maybe someone could help me out.

I just bought a 800-900 lumen flashlight that uses 2 x 18650 batteries. The darn thing is really bright and I'm really happy with its performance. However, after using it on high for 4-5 minutes, it shuts down suddenly. This happened twice.
Initially, I thought I'd fried the LED but after inserting fresh batteries, it worked ok.

When examining both batteries after shutdown, one cell measured 4.15 v. and the other one, zero (0) v.
This happened both times (protected cells). Could it be that I need to be using better quality batteries?
I'm using the "Trustfire" batteries which I bought thru the net.

I would really appreciate some expert advice here.

Welcome to CPF, Joe!

The protection circuit on one of the cells is tripping out for some reason. Put it on charge for a few seconds then take it off, take another voltage reading and post here again to let us know what it is.

The cell at 4.15V is still 95% fully charged, so you don't need to do anything with it for the time being.

Thanks for a really quick response.
I put the cell (registering 0v.) into the charger for an hour already (it usually takes 5 hours for full charge).
Just pulled it out and it measures close to 4.2v. What does this mean?

With Li-Ion cells, 4.2V = fully charged. That means the protection circuit tripped too early, maybe because of too much current draw. Some cell brands have a low current threshold, but I don't know what current your light might be drawing, as you haven't said what it is.

When a protection circuit trips, the cell will read 0.0V until it is reset. A small jolt from the charger for a few seconds will reset it.

from Your explanation, it is clear the protection kicked in,
only - with a 2 cell light - the typical "800 Lumen" light should not draw enough current to have it kick in
(thats only 1.4 A)
:thinking:

I suggest this to be moved to the electronics & batteries subforum since it looks to be a battery issue.


Average Joe, it is possible that the second battery is defective and has got a very low capacity, thus being emptied far too soon and being charged back up to full in only one hour.

Whatever it is, be aware that using a possibly defective Li-Ion battery is dangerous and if you decide to do further testing you should be very careful and never use or charge that battery unattended.

In order to find out more about that battery it would be useful if you could discharge it again until the light shuts off and put it in the charger for a few seconds only, then measure the voltage immediately.
It would also help if you could measure current draw of the light. To do this screw off the tailcap, set your meter to the 10 Amp setting and measure across the contacts on the light's body and the battery that would be connected by the tailcap in real use.

I highly recommend getting quality batteries. AW, Redilast have been recommended here on CPF.

^^^ WHS

I have to discard several faulty ****fire 18650 batteries because of similar problems - it's not worth the risk with li-ion batteries.

Thanks guys, I really appreciate the advice. Btw, I've already ordered some (better quality) batteries.

Funny this is... when I put these same ****fire batteries into my Scorpion V2, it seemed to work fine.
I read somewhere that the V2 pulls over 2 amps in turbo mode (2.4amps, I think). I wonder why that should be (??) that it works fine, I mean

maybe there is some kind of a short additionally?

What if You change the position of the cells?

Use AW or Redilast 18650 cells. They can take the current. AW IMR CELLS would work as well. I've quit using ****fire batteries because of problems like this. Use them up in your other flashlight or throw them away.