That’s definitely not normal. They have very little thermal mass and should cool down to room temp in 15-30 minutes. If they’re still warm they still generate heat … sounds like an internal short perhaps. Discard the cells, and don’t keep them in your home or somewhere they could start a fire until you do … just to be safe.
Which charger?
But anyway, the battery behaving anomalously is probably effed, I would not try to use nor charge it again – better to discard it safely and get a new one.
I can’t recall. It’s a soshine 2 cell charger
Can’t you just look at the charger and find out what charger it is?
Do you not have access the charger anymore? 
Yes but I’m not home now
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Not a really reputable brand. It’s more than possible that it’s been slowly effing up your batteries. I would get a new one from a known-good brand and model along with the battery you’re replacing.
Coincidentally there are two active threads here on BLF talking about good chargers:
Good luck!
That would make sense. These batteries haven’t been used hard through the years. They should have hundreds if not thousands of charges left in them.
Li-Ions are usually specced for about 500 charge-discharge cycles, so unless yours are something special like LiFePO4, “thousands” should definitely be out of the picture…
- Get a charger with voltage read out, and/or a digital multimeter.
- Never charge Li-ion batteries at night whilst you are sleeping.
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So, my opinion:
Get a decent multimeter. Do not buy cheap stuff, it can be inaccurate, and with li-ion batteries you need fairly high accuracy (something like 0.05v difference can be important). This is generally useful thing to have anyway and will last for a long time.
Do not discard cells right away. Check voltages, see if the cells are self discharging fast or are overcharged, only then decide what to do. If nothing else just for the sake of curiosity.
Check what the charger does. Make sure it stays within safe voltage and stops charging correctly. Potentially - just get a better charger.
Also… “thousands of charges”? Not going to happen. 300-500 from new would be reasonable. With standard removable cells like 18650 it makes very little sense to use them all the way to failure. They are very cheap and become less stable/safe as they age, once capacity loss becomes noticeable it makes sense to simply replace them.
I’ll take all this info into my arsenal. I work in the trades and own two Fluke meters. I’ll start checking cells with my meter and I will get a better charger. Also I’m guessing I’ve charged these cells probably less than 20 times since I’ve owned them. The lights they were bought for were used for riding my bike at nights and that wasn’t something I did regularly. We took the family on a ghost hunt tonight so I was charging all my batteries to get my lights ready.
What is it about lithium ion batteries like my Dewalt and Milwaukee tools rhat I can put them in the charger and walk away and they are ok but these protected 18650 cells you shouldn’t?
I actually wouldn’t leave power tool batteries charging overnight either. Some of the chargers have protection that’s supposed to prevent bad stuff from happening, but like has been mentioned, it’s better to be safe than sorry. I always practice unplugging all my li-ions as soon as they’re full.
Technically you should not leave any li-ion battery charging unattended. Be it loose cells, power tool batteries, phone, laptop or whatever. Any of them can catch fire and if you google for example “milwaukee battery fire” or may be “explosion” instead of “fire” you’ll surely find videos of it happening.
It is not always practically feasible though, but you should still understand that each time you do it you take certain risks.
Then there is the fact that power tool batteries usually use high quality cells and have multiple levels of protection. Phones are similar. They often use much more advanced protection circuits too, for example preventing user from shooting themselves in a foot by disabling charging when the battery is too cold/hot.
Typical protection circuit in 18650 would prevent over/under voltage and short circuit, that’s it. And unlike phone or power tool pack which have built-in chargers you are using a charger of unknown quality too, so not 100% sure that it will not do something bad.
Another question then - were they overdischarged by any chance at some point? If you store li-ion battery for a long time, especially protected one since protection circuit has parasitic drain, it can be overdischarged and once it gets below ~2.5v it is no longer safe to use and is basically ruined.
I wasn’t aware that the protection circuit created a parasitic discharge. I did not know this. Some of these batteries have been sitting on my bench for several years. I keep my batteries fully charged prior to storage and I was not aware that they would discharge like that. I typically would take them and put them on my charger to top them off if they have been sitting a while, but I never knew they would drain down to that point. It’s possible that’s what happened.
It’s just a general safety rule. “Don’t charge cells unattended.” The idea is that if there is a fire you can put it out.
Once a charger finishes charging a cell, the charge cycle is terminated and nothing should be happening electrically, although some chargers have a slight parasitic drain.
Most cells are rated to be discharged to 2.5V. That is the specified cutoff voltage in the datasheet. The “do not recharge” voltage is lower. <2.0V is “do not recharge” territory.
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If you read the manual it probably says not to do that lol. But most tool battery chargers don’t fully charge so they can handle being left in the charger better. They usually stop just after like 4.1v. Except 12v tool batteries, those do fully charge. M12 batteries go to 4.2v, sometimes little higher. Either way tho, not ideal really
Anyways, ya that battery is trash recycling, and soshine is pretty sketchy
The protection circuit at the bottom of the cell needs power and runs a small insulated metal strip alongside the battery to the positive terminal.
If that insulation gets damaged in any way (e.g. by a drop) you could have an instant short on your hands. That’s something that won’t happen with unprotected cells.
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So question, I put a fluke meter to both of these batteries this morning and one read 3.77 and the other read 3.27. This is after having each one in a convoy flashlight at the same time yesterday both on high trying to discharge them for maybe 35 minutes before I shut the lights out and swap the batteries For actual use. One convoy is a 950 lm and the other one is 500 so that might explain why one battery is a little lower than the other. Does this sound odd? I would assume even after 30 minutes on high these batteries would be lower than this. Is it possible these batteries are still good and I could buy a good charger and keep using them? How would you know if they are baked? As hot as they were yesterday (at least the one), logic says yeah it’s garbage but now I’m starting to wonder if they aren’t still good but I don’t know how you would know what’s actually going on inside each cell. I sure don’t want to hurt myself or my property.
Numbers are fine NOW but probably were not fine yesterday. Don’t risk it, LiIon cells are cheap(ish). Especially the extremely hot cell surely took some damage: e.g. mobile phones make sure they do never get hotter than ~50°C.
At >80°C physical damage will definitely occur and the cells may go 
the next time you charge or use them.
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The issue with leaving these unattended while charging has been how long they take. I have charged these cells in the past when the convoy started flashing indicating batteries were low, and they have taken many hours to charge. Certainly this isn’t something I have time to monitor a charger for 4-6 hours. I get that they shouldn’t be left unattended but wish there was a way to safely charge these and not have to babysit the thing. Maybe it would be more convenient for me to start researching different lights and power options? Seems like using cells like the 18650 require a lot of time and patience and I am constantly busy with other stuff.