18650 batteries - LVP at 2.2V OK?

I have a fan that uses 18650’s but the low voltage protection only kicks in at 2.2V. Is that safe? I don’t think it’s good for the battery, but are there safety concerns if using this around my family? Like letting the fan run over night while camping and perhaps letting it run down?

I don’t intend on making it a regular practice to damage batteries, but if it accidentally happens, I want to make sure I’m not endangering anyone.

None of my protected 18650’s fit the battery compartment - too long. Are there special short protected 18650’s?

2.2v is a little low. 2.5v would be the very least I would suggest, 2.7v would be better.
Most of the time Li-ions that have problems happen while charging or discharging at too high of rate.
I dont feel discharging them to low will cause a problem at that instance but you are degrading the battery and it could eventually cause problems while being charged.
Once the internal resistance increases from being too deeply dischaged repeatedly then a problem could arise when charging.
I would be more concerned if the 18650’s are used in series. I’m guessing they’re run in parallel to gain extra run time.
HKJ has test data for a lot of different 18650’s which included their dimensions. You might find something protected that would fit. I seen a few in the 67.5 to 68mm range in length.
https://lygte-info.dk/info/batteryIndex.html

There are some experts on this forum and I am not one, but here is what I have read. Deep discharge will increase the resistance faster and result in more capacity fade. Still, some forum members deep discharge their batteries routinely and have good results. IMHO your batteries will not last as long.
But as far as danger issues, keep an eye on them when they are being charged since that is where most issues arise. If they are charging much slower or heat is being generated, recycle them. In addition, the best approach is to check the voltage with a DMM regularly and charge them at around 3.4 or 3.5 volts and bring them up to around 4 volts. This will make them last longer and stress them less. The DMM is your best safety tool if you use it.
Others may have different opinions and they will be helpful too. This simply reflects my methodology.

Would you happen to have a link about deep discharge and increased battery resistance?

I think I’ve also read something about the time spent in deeply discharged state (eg. 12 hours of the battery at 2.2v, versus several days or a few weeks of having an 18650 sitting idly at 2.2v. Usually I notice voltage increases when unloaded, so I’m also uncertain whether it’s the 2.2v LVP when loaded (ie. voltage will still increase while ‘idling’)…

There was an investigation about battery life, but they only discharged to 2.5v.
2.2v is quite low (as 007 said above) and is not within the scope of this study, but here it is:
From another thread:
docware wrote: The study is dated 19.4.2017, cells are Panasonic NCR18650PD. You can read the whole study here :

Focusing on battery resistance, it found “microcracks of the NCA cathode and weakened particle contacts are assumed to aggravate with larger cycle depths and cause the marked impedance increase.
…the mechanical stress onto the graphite active material can be an explanation for the accelerated aging when cycling to lower SoCs.”
Of course, they were looking at all contributors to aging not just resistance increase, so many other factors are described in the study, like changes in the electrolyte and anode issues.
Hope this is an accurate portrayal of the article, please correct me if there are any issues.

The latest generation 18650 cell’s has a marginal larger capacity.
In my personal opinion that is caused by the ability to survive a deeper discharge (2.8V > 2.5V).
The remaining capacity between 2.8V and 2.5V is now useable without causing too much harm.

Though not for everybody and in all circumstances I think: an occasional 2.2V won’t hurt.
That is: if the discharge stops during the night and you recharge the next morning.
Because discharge is a chemical process. The current may stop, the chemical reaction can go on.
The longer the state of deep discharge lasts, the greater the possible permanent damage.
I would advise to test (all) your cell’s once in a while.

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If you prefer protected batteries, these SOSHINE 3,600mAh are the shortest 18650’s HKJ has tested

Thanks Henk, that is good to know.

Deep discharging li-ion isn't that harmful. Of course it all depends, namely how deep is the discharge. When even big manufacturers state “2V” as a valid minimum discharge voltage for their cells (LG HE2, Sony VTC6A) you know very bad it can't be. It may not be the best practice, but what really matters is not going down to 2V, but letting batteries dwell below such voltage.

If your fan controller (or whatever) cuts off at 2.2V that's fine. You can recharge the cell as soon as possible if you do care about lifespan, but bear in mind too that higher voltages (4+V) can be even more harmful. See: BU-808: How to Prolong Lithium-based Batteries.