“Is there any way to revive an over-discharged Li-Ion 18650 battery?”

Not a good idea.

The protective circuitry (in the Li-ion battery or in the device that the battery powers) is designed to prevent dangerous over- and undercharging, which can cause the battery to overheat and catch fire.

(Remember all those hoverboard fires a couple years ago? That’s what you get when you abuse a Li-ion battery; or its self-protections fail.)

Li-ion protective circuitry requires at least a little battery power to energize itself, so a Li-ion battery typically reserves the last 3-4% of the battery charge for internal use. That way, when a low-battery condition forces the device to shut down, the battery still has enough power left to keep the protective circuitry alive and ready to accept the next recharge.

But if the battery is drained so far that the protective circuitry goes dead, the inert circuitry prevents normal recharging — a “fail safe” measure to ensure that the battery can’t be recharged without the protective circuitry alive.

So: When a Li-ion battery won’t accept a charge, it’s no longer safe to use.

Can you get around it? Maybe, with the right tools and knowledge. But you’re asking for trouble: Again, remember those hoverboard fires?

Besides, why would you take the risk? Individual 18650-sized Li-ion batteries/cells aren’t expensive: The ones in the photo above cost about $6 each, and last for hundreds and hundreds of recharges.

Is it worth risking a fire to save $6?

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