At what point is a heater a heater?

Is there a consensus on a temperature at which a cell is officially a heater and needs to come out? (Before the fuse wire breaks of course! ) And conversely, what is the hottest you've had a cell at and not considered it a heater?

Many will have different opinions and there is an obvious grey area in there, but I hope that a pattern will emerge as opinions are given!

Thanks!

There's a few threads on this topic. There needs to be some classification as to when the cell is getting hot.

* Getting hot during charge
* Getting hot during discharge
* Getting hot in the charger or the pack

The majority have a noted cell charge in the charger at a temp of about 60C. If the cell reaches 60C, it needs to be pulled. Getting hotter than that starts to make the heatshrink smelling, possibility of melting hot glue if close enough (I've had this happen as the heat transferred through the cell holder metal tabs and make the TP4056 chargers become unattached to the holder by the hot glue)
Now, if the cell is being discharged, they probably shouldn't get hotter than about 50C, I would guess (not entirely sure on this one as I haven't had to go down that route yet)
If in a pack, I wouldn't want the cell to get hotter than about 45C

Generally, a cell is a "heater", a term which I don't like at all, when it doesn't reach its end of charge voltage while charging and turns most energy into heat instead of storing it. This is unrelated to its temperature. The cell will consequently get hot because of this but the effect can be seen long before the cell gets hot.

Thermal cameras are good for detecting heaters. They stand out clearly from the rest (bottom-right corner).

I would also look for a large voltage drop when connecting a load.

As an example, using my constant current tester at 1A, if a cell drops down has a delta of 0.3V instantly, I just throw it out. Useless otherwise.