I've got a Li-ion battery (LGDBHE21865 Q153F022A2) that has no protection circuits (as far as I know). The battery can support a 20 A current. I used it in my vape device some time in the past, but then the battery was lying on the shelf for a long time and it has discharged to approximately 0 V (may be ~0.5 V). I charged the battery (using a charger with about 0.5-1 A current; the charger has a special signal when a battery is completely charged) and set it up into my vape again. Device shows 100% battery level even after 10 minutes of intermittently using at ~35 W.

My questions are:

  • Is it still safe to use the battery after being completely discharged and then charged again?
  • Does it mean that the battery has some protection circuits that rescued it from losing capacity? Or should I test the capacity in a more accurate way?

Enter image description here

  • 2
    \$\begingroup\$ It would be reasonably safe to use in a low discharge rate application. Hard to say if it is still safe for intermittent high discharge. More important than a capacity check, in my opinion, would be an ESR test or temperature test. How does the ESR compare to a new cell? Or, if you discharge it at 20A for 30 seconds or 1 minute how hot does it get? Is it different from a fresh new cell? That will tell you whether it is still safe in my not expert opinion. \$\endgroup\$
    – user57037
    Apr 22, 2021 at 20:45
  • \$\begingroup\$ Ditto thermal effects. If you have another one of these, run them both in the vape until discharged, then recharge both. If this one gets hot and the other one doesn't, then it was damaged. It likely has a small protection circuit in it, under the positive cap. \$\endgroup\$
    – rdtsc
    Apr 22, 2021 at 21:03
  • \$\begingroup\$ That cell does not have a protection circuit in it. \$\endgroup\$
    – user57037
    Apr 22, 2021 at 21:56

2 Answers 2


No, it is not safe to use, and you should discontinue use of that cell immediately and store it in a fire-proof container.

Normally, protection circuits will have a 'fuse' function that will permanently disconnect the cell, effectively destroying it (unless you bypass the protection circuit, which you shouldn't).

Any Li-ion cell of that chemistry is destroyed if it is discharged below 2 V, and most certainly to 0 V.

The reason for this has nothing to do with if it charges fine or not. The reason is that once the cell drops below 2 V, metallic dendrites begin to form inside the cell. Think of them as tiny, crystalline spikes.

When you charge the cell, lithium ions physically move from the cathode and intercalate (wedge themselves in between) the atoms of the graphite anode. This causes the anode to measurably increase in size slightly, which pushes the metal dendrites into the membrane separating the cathode and anode.

Eventually, the membrane will rupture by this repeated mechanical damage from the dendrites being forced into the membrane each charging cycle. This causes a dead short inside the cell, and it will vent (explode) and ignite the flammable electrolyte inside it, resulting in a chemical fire that is all but impervious to standard fire suppression systems and that only burns more vigorously when exposed to things like water.

When this actually occurs is unpredictable and does not necessarily occur during charging, but only sometime after. In other words, it could occur after you recharge it and slip it into your pocket or bag as you go out. There are plenty of videos of exactly this occurring to vape users and I am sure a fair portion of these accidents (which always seem to occur when the vape is not in use - which means overcharging or using after overdischarging) are the result of people doing exactly what you seem to want to do - continue to use an overdischarged battery, thinking it was safe to use or otherwise ok simply because it seemed to charge and have most of its capacity. Neither of those things are useful metrics and that cell is now dangerous, especially in the charged state, and you have no way of knowing when it will fail (spectacularly).

Enter image description here

Vaping is an application that typically requires unprotected cells due to the high currents required, currents that are difficult to make protection circuits in such a small size that can handle those currents. This is why vapes typically use unprotected cells.

There is nothing wrong with this, and it is not a problem unique to the vaping community. I myself have unprotected 26650 cells in some LED flashlights with "enthusiast" levels of brightness that require unprotected cells due to current draw as well.

But without protection circuits, it does require the users to observe and respect the same safety limitations that would otherwise be imposed by a protection circuit. Do your due diligence and it is no problem. Stay safe!

  • 1
    \$\begingroup\$ The only thing I really object to in this answer is the way everything is stated as a certainty. You say the dendrites will form (not may form). Then you say they will rupture the separator (not "may" rupture the separator). If you get dendrites, the ESR will increase, and the cell self-heating will increase. If you are able to test that and compare it with a fresh cell, you can conceivably continue to use the cell. Otherwise best not to. \$\endgroup\$
    – user57037
    Apr 22, 2021 at 22:02
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    \$\begingroup\$ @mkeith I strongly disagree. They could conceivably continue to use the cell, but just not safely because there is no easy or foolproof way to know, as you yourself are arguing. When it comes to safety, one needs to assume the worst, and I used words that convey certainty because saying thats like what you're saying in your comment has the potential to cause an accident. Additionally, I do not think there is any 'may' involved in dendrite growth. All it requires is a nucleation point, and after that, it is just crystal growth. As far as a know, that is not a stochastic process. \$\endgroup\$
    – metacollin
    Apr 22, 2021 at 22:19
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    \$\begingroup\$ Also, the chemical fire is not "all but impervious to standard fire suppression," and it does NOT burn hotter with more with water. Fire fighters employ copious amounts of water to extinguish tesla car fires. This works well because it cools the cells down and extinguishes the flames, both of which are helpful. When the batteries ignite, it is a fairly standard fire burning in air. Cooling the batteries and/or removing oxygen will both help to extinguish the fire. \$\endgroup\$
    – user57037
    Apr 22, 2021 at 22:36
  • 3
    \$\begingroup\$ Thank you @metacollin for detailed explanation. Of course it's a safety problem thus according your recommendations I will not use the battery anymore. It matters especially when the battery is used in a vape device which contacts with human body. \$\endgroup\$ Apr 23, 2021 at 5:51
  • 2
    \$\begingroup\$ Also to @mkeith, this article on BatteryUniversity is relevant. The difficulty of putting out fires with water metacollin referred to lies with batteries having substantial metallic lithium inside. Li-ion cells, as stated in the article, have little metal Li inside, so are quite safe to extinguish with water. \$\endgroup\$ Apr 23, 2021 at 18:10

It's not safe to use an overdischarged lithium ion cell. This is why you need a BMS for things like a battery pack. Of course, a BMS cannot fix quality control problems where the cells are not matched. It is there to disconnect the load when the weakest cell reaches the cutoff voltage. Otherwise, the pack will be destroyed. Even the humble NIMH is not totally forgiving either. I had this problem with 2 cells in a pack of 8 but for some reason I was able to get those 2 to come up with the others. Keeping my fingers crossed for the other set.


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