26650 battery question. Dropping to 3.5v soon after charging.

I am new to 26650 batteries and have a question. I got an Ultrafire 26650 and a Tangsfire 26650 from Tmart. The TF charges up to 4.2v and seems to hold it there like a typical 18650 but the UF charges up to same voltage but quickly drops to 3.5v after just sitting out of the charger for a day or so.

Is this normal? I see the 26650s are marked as 3.2v unlike my 186650s which are marked 3.7v. The UF seems to work fine but I have never had a cell act like this and I am new to 26650s. I am not new to 186650s so that’s what I am comparing them to.


Now that’s out of the way, the reason why it’s rated at 3.2V is because it’s a LiFe cell, not a LiCo one. The 4.2V charger was designed for charging LiCo ones, but it definitely overcharged the LiFe cell to 4.2V.

You should be thankful LiFe chemistries are safer and do not explode as readily as Lithium Cobalt cells. Damage has been done to the cell, and you should toss it out before something worse happens.

How many charges have you given the LiFe cell?

Whoa! I didn’t expect to read that. I have put it in my Xtar WP2 about 3 times. Once, when I first got it, then twice to top it off. It has seen maybe 3-5 mins of actual use.

I was under the impression that my Xtar WP2 would safely charge these 26650s. I saw someone here posted pics of their 26650 in one.

Are you telling me, I need a special charger for my 26650 cells apart from my Xtar?

yeah the Ultrafire 26650 is marked 3.6V at full charge (see 4th pic). You could charge them with a Hobby Charger.

Or if you were diligently watching the charge and pulled the battery from the charger when it reached 3.6V, tested with a DMM (digital multi-meter) of course. I charged ~60 18650s like this. I didn't want them stored at full charge, so I pulled them at ~3.5V.

The LiCo TangsFire 26650 has got the normal voltage range (4.2-2.7V), but the capacity (6000mAh) is not realistic. **See HKJ's explaination here.

In the future you might consider some King Kongs. KumaBear sells both protected and unprotected ones here

You mentioned some 18650s which are marked 3.7V. That refers to it's nominal voltage. But they really are 4.2V at full charge and should only be run down to 2.8/2.75V, and no more. Nominal, meaning in name only.

Another example is the naming convention of your 18650 Li-ion. Your 18650 batteries should be exactly 18mm wide by 65mm long. But many cells are actually a bit longer, especially if they have protected circuits on them.

Yup, MRT and HKJ basically nailed it. 18650 and 26650 are sizes of cells, just like AA or AAA.

3.7V (nominal), 4.2V (charged) and 3.2V (nominal), 3.6V (charged) are the voltages of the cell, which depends on the chemistry.

There are 3.2V/3.6V 18650’s and 26650’s just like 3.7V/4.2V 18650’s and 26650’s.

Unfortunately, I wouldn’t recommend MRT’s way of charging because it’s too risky. Some li-ion chargers have 3.6V and 4.2V switches so that the charge voltages can be selected depending on the cell chemistry, or you can get a hobby charger too as MRT had stated. LiFePO4 (3.6V) are more tolerant of abuse, but damage has been done to your 26650 cell and you should toss it.

Stay safe!

I had no idea the 26650 came in two voltages. I don’t like 26650 anymore.

alot of battery sizes come in a few different voltages. look at aa and aaa size batteries theres probably a half dozen different nominal voltages between chemistry’s, if not more. you just need to know what chemistry you are buying, and have a proper way to charge that chemistry

16340,14500,18650 and 26650 all come in two flavours. Li Ion at 3.7v, and LiFePo4 at 3.2v.
It was just a matter of you ordering LiFePo4 cells by mistake. What is called a life experience. Now you know and will never forget.