Yes, in fact it was I who did the wrong thing, the Ultrafire cell behaved perfectly, not even getting slightly warmer. 8)
Iām amazed weāre at post 21 and no oneās pointed out what a bad idea ultrafire cells areā¦.
Thanks PilotPTK and totilde. I might try resetting the protection circuit when the new 18650 arrives - I havenāt thrown the old one away yet, taking care to connect + to +, or - to - for just about one second. I think, though, I had better read more about Lithium Ion cells
I see some good information at:
http://flashlightwiki.com/Rechargeable#Lithium_Ion*.28Li-ion.29*-\_3.7V.2Fcell
I was just thinking I had better mark these cells in some way so they donāt get mixed up with other cells I might buy for a 2 or 3 cell 18650 torch, because I believe you are not supposed to mix used and new Lithium-Ion cells, or of different voltages in multiple-battery flashlightsā¦ā¦
From what I gather there are fake Ultrafire batteries on the market, see:
ā We are the manufacture of Ultrafire collection,and here declare that we had not manufactured over 3000mAh above for #18650 rechargeable battery,we do not accept any responsibility whatever in respect of fake products.ā
and then, for example, the 1300mAh rating for what are alleged to be 3600mAh Ultrafire 18650s at:
So I can imagine Ultrafires might get a bad name, I see what you mean. But I think the main thrust of this thread is that I need to know more about Lithium-Ion batteries, and that I should never use unprotected cells.
Certainly brush up on lithium doās and donāts scaru has written some good reference threads that are well worth a read.
Iām just unconvinced that ultrafire.net is any more the real ultrafire than anyone else, personally I would stick to Panasonic, samsung, sanyo based cells myself. Iāve got a couple of ultrafire cells that came with my first light purchase but they have now been retired in favour of cells that give much truer capacity. 
I was worried about him running the cell until it quits or is shut off by the protection circuit. I try to keep my li-ions above 3.8v. I thought just relying on the protection was dangerous.
Yes, I had read that somewhere recently, so thatās why I bought the DMM.
Run them down āto the point where the LEDās stop producing any lightā NO, stop doing that!
I will defer to everyone else here, but I was always told to stop using the light and recharge WELL before you ran down a Li-ion to that point, when you see the output drop very rapidly or to less than 50% of full brightnessā¦pull them out and charge them.
On a good charger.
Most driver low voltage warnings are at 3v. I tend to have an idea how much use a cell has had so I just pull them and check then charge when it feels right, I do suggest picking up a nanjg based p60 drop in for this reason if not for any other. The peace of mind that the driver wil warn before protection trips is nice and you can lose visible pwm and blinkies at the same time. 8)
Yes, thanks. I realised there was a danger that I might be overdischarging, so I bought the Digital MultiMeter intending to check the discharged voltage.
A real world cell can be thought of as an ideal voltage source of V volts in series with an internal resistor of R ohms.
Measuring the open circuit voltage with a voltmeter is safe and gives you the value of Voc.
Ideally, you could put an ammeter [whose internal shunt resistance is zero ohms] across the battery and get the value of the short circuit current Isc which gives you Rint since Rint = Voc/Isc. Now the cell is completely defined. Itās the Thevenin Equivalent Circuit.
But, most batteries donāt like being shorted. Isc for a car battery may be 12.76 V/0.01 ohms = 1300A.
Another way to characterize a battery at some load current and temperature is load down the battery with a resistor so that Voc drops maybe 10%, measure the voltage across the resistor, and calculate the internal resistance. Then youāll have Voc, Isc and R. Let me know if you want the formula.
Thanks, gords, I found Scaruās thread on Lithium Ions:
Well, Iām no expert, (obviously!). I note your comments, although I felt the 18650 I bought from the Ultrafire shop had respectable charge and discharge times, (which I assume means it had OK capacity).
Drivers are another issue I must learn more about.
Thanks for the tip 8)
Thatās really not reasonable. The nominal voltage of a lithium cell is 3.7V. That is the voltage that a charged cell is expected to produce at its rated capacity. There is very little capacity difference between the fully charged, unloaded 4.2V and the nominal 3.7V Only discharging them to 3.8V means you are not using over 80% of their capability.
ā¦ maybe he refers he store them over that voltage when he puts them away.
if he refers to use them only from 4.2 to 3.8ā- its a no sense.
stolen from cpf
Best to recharge at 3.6 volts, they donāt have any capacity left then, and you may damage the cell if you discharge to 3.5 volts.
This only applies to li-ion,
4.2V is 100%
4.1V is around 90%
4.0V is around 80%
3.9V is around 60%
3.8V is around 40%
3.7V is around 20%
3.6V is empty
going to 3.5 volts will damage the cell.
Actually it makes perfect sense.
At 3.8V with no load, the Sanyo UR18650FM has a remaining capacity of about 40%. At 3.7V its down to 10%.
Also, nominal voltage is with load.
Moar CPF I guess Iām just A little (lot) OCD Low voltage on 18650 cell | Candle Power Flashlight Forum
i never understand why people say under 3.6v unloaded will damage a cell. i have been primarily using unprotected trustfire flames for well over a year now, maybe even pushing 2 years. and i have ran them down around 3.2v a couple times and have not noticed any capacity loss. no heat while chargingā¦
Ahem.
(HKJ's picture)