Lowest safe rechargable voltage of a 26650?

Batteries and Chargers Rechargeable Batteries
1

Hi All,

What is the lowest safe voltage to discharge to using a 26650 and even a 18650 as my next torch that’s coming will use this sort.

I’m sure this has been answered many times but have searched all over and the result varies from 2.5v - 3.0v. Just received my Ultrafire torch from eBay and this is first time using unprotected lithium batteries. On the side of the ultrafire battery it states “the voltage of full charge and empty condition is 4.2v and 2.75v”. What do you guys recommend to be the lowest safe discharge?

I purchased a Nitecore i2 charger instead of the rubbish ones they come with. I’ve read many stories of these venting, flaming, exploding while being charged. What is too low to safely charge from without danger?

If the included charger was ever used, is it safe? Do they turn green at exactly 4.2v and keep charging or do they shut off?

Using the 26650 in a torch how will I know when I should shut the light off to stop it discharging too low?

Any help is appreciated

2

If you just drained it down to 2.7…recharge it, just do it at a slower rate at first as to not overly stress it

3

I can’t charge at a slower rate than what the charger is set at which is 500mA. At that what is safest?

Thank you for that link and info :slight_smile:

4

There exist no single answer to that, because it depends on the actual LiIon chemistry.

In most of my testing I uses 2.8 volt and has not seen any bad effects from that.

I have killed some batteries discharging to 2.5 volt and others has no problem with it.

5

Would any of the lithium torch batteries be only discharged to 2.8v safely? Love the torches and thinking of getting a few for family so needing to know for 18650 and 14500?

6

Many 18650 batteries cannot be discharged lower than 2.8 volt, but Panasonic 3100/3400mAh can surview 2.5 volt.

7

It is not only related to the charger but the flashlight as well. If it is a high amp draw light then you will have a lot of voltage droop particularly when it’s nearly flat. Resting voltage might read 2.7v but when it was under load in the light, it will read lower still. If the flashlight is not drawing that much amperage from the cell then it is not much of a problem at 2.7v

8

Look at discharge graphs. HKJ has a LOT on this site.
There is no real capacity left after 3.0v. There’s not much after 3.2-3.3. The lower you go the more you stress the cell and the shorter the effective life. It’s a rechargeable, why push it?
If you wanted to maximize the LIFE (not the maximum use range) of a cell you would keep it between 3.5-4.1v, and try to not keep it over 4v for prolonged periods. Both sustained/prolonged charge (especially in warm surroundings) and over discharge damage the cell.

In a torch the light will likely start dropping dramatically around 3.0-3.2v.

This is important:
[On the side of the ultrafire battery] - so we know right off that your battery is most likely crap. Anything *fire is junk until proven otherwise, IMO that includes the charger.
You actually don’t have any idea what ANY charger will do until you test it. The probability of a known good brand is having a high level of confidence in successful operation. *fire might work, it might not.

9

You know what this means, right?

“Copper shunts may have formed inside the cells that can lead to a partial or total electrical short. If recharged, the cells might become unstable, causing excessive heat or showing other anomalies.”

You don’t want your family at risk, obviously.

If you don’t understand this risk, don’t do that.

10

I think you are asking if the torch would shut down to prevent over-discharge?

I'm afraid that is completely up to the manufacturer. Some lights have a cutoff which may occur around 3.0v or slightly under but many do not. For some lights there may be a sudden drop in output indicating that voltage has dropped to a critical level; others may dim gradually or step down a little at a time. We would really need to know EXACTLY what you purchased. Or you could try to find reviews on a light before you buy it.

Best way to prevent overdischarge is not to leave the light running unattended and charge often. Barring the issue of keeping the cells over 4V in high temperatures, the best long-term life will come from partial discharges rather than draining completely each time.

Also, as you seem to be new here, please make sure you understand the dangers of Li-Ion chemistry. Especially as you talk about getting lights for the family, who I may assume have only been exposed to regular Alkaline or NiMH cells up till now? These Li-Ions are not for casual use by the uninitiated.

Finally, PLEASE stay away from cheap ****fire cells and chargers found on ebay and budget online dealers. Invest in some good quality Panasonics, Samsungs, etc. There are plenty of useful threads here to help you decipher it all.