Sure it can when not protected. Also, what you are doing is dangerous. Just think what happens if one of the PCBs fails. ;)
V-Spec: He deep discharged them with a hobby charger before, so there wasnt really much energy left in it. Of course its not advisable to do so unless you know what you are doing..
1) Test and measure all the cells.
2) Don’t buy cheap crappy 18650s, always check battery reviews first when going to shop for batteries, there are some **Fire that don’t suck, like the TF 26650 Flame but that’s about it.
3) Get Sanyo UR18650FM or some type of Panasonic of your preference. The price is not that much higher compared to rubbish TFs, UFs, …
It is safe, even with unprotected cells.
So reverse charging is a myth?
You can think of it as an open circuit. Two cells in parallel - positive pole not connected to anything.
You do not get any reverse charging with the above setup, it is a parallel connection, exactly like the picture below:
And you do not even have a connection if the light is off.
Indeed, that makes sense for two-cell lights. What about lights with more than two cells? I'm having a hard time imagining such stuff early in the morning. :D
If the batteries connect, you will get a lower voltage to the light, i.e. with 3 batteries the light will only see the voltage from one battery.
And how would they be drained?
With 3 batteries, one of them would be overcharged.
So that would not be recommended then.. its OK for 2-cell lights but not when there are more cells involved.
Yes, 2 is perfectly fine.
Other even numbers can be used, but requires that the batteries has the same voltage, odd numbers is not a good idea. I will not recommend more than two batteries, because a mistake in orientation is bad.
Here I have draw the circuit, the red box is a resistor that simulated the head of the light.
As can be seen two and four batteries is just parallel. With four batteries you could also have 3 one way and one the other way, it would give the same problem as 3 batteries, just worse.
That made it clear. Thank you very much for your effort in enlightening me. :)
I don’t understand why am I still able to operate the 3T6 with the defective battery. I on it and it was definitely very very bright. Fortunately, it did not explode yesterday or else I will not be here today.
I hope you didnt put the cell into the light again since yesterday..
Anyway, LiIon cells usually dont die right away, most accidents happen while charging.
I still value my hand. I even kept it inside my new safe (which has nothing in it except the 18650). I figure if it explode, my house will be still intact.