Are over-discharged lithium cells safe? (And how to test for damage.)
Why Electrical Engineering Stack Exchange recommends it
Electronics Stack Exchange answerers and commenters link it when discussing whether deeply discharged Li-ion cells are harmful or unsafe to recharge, citing it as a counterpoint to the older belief that they are ruined.
Recommended by 0 people across 0 different months, 2018 to 2023.
What it is
BigClive investigates whether lithium-ion cells that have been fully over-discharged, such as the flat cells found in cheap Poundland power banks, are actually dangerous or permanently damaged. He walks through a published research paper on over-discharge and shows practical ways to test a cell for damage.
What people said
Cites Oskar Skog · 2018-03 · Electrical Engineering Stack Exchange · on “If Li-Ion battery is deeply discharged, is it harmful for it to remain in this state unused?”
Bigclive [this video] says there won't be any internal short circuit before the cells have been reverse charged to -12% which equals to about negative 2 volts. It will grow nasty copper spikes if the cell gets pushed beyond -12% (-2 V), then it's dead-dead. The research he found [LINK] The main concern is with series connected cells: they're not perfectly balanced, so when one goes flat the others will reverse charge it and potentially kill it or at least weaken it. Of course, they're not going to be happy about being drained to 0. This just says that it's a lot less worse than what was previously believed.
Cites Pau Coma Ramirez · 2020-06 · Electrical Engineering Stack Exchange · on “Undervoltage protection strategy for Li-ion batteries”
Answers: is it safe to rely on the built-in safety PCM of a Li-ion battery? Of course nothing is 100% safe but we do the best we can. 2.75V as cut-off gives a bit of margin over the "typical" minimum discharge of 2.5V. Even discharging further, dependind on the discharge characteristics (fast/slow/pulsed/...) , according to this study [LINK] Dischargin further should not be much of an issue, and detectable durring charging if it is a problem. If you are still in doubt, I would get a certificate from the company that is providing you the battery describing and certifying this feature and in case there is a problem you are covered. does it damage the battery to actually reach the built-in safe
Cites Martin Andersson · 2023-08 · Electrical Engineering Stack Exchange · on “If Li-Ion battery is deeply discharged, is it harmful for it to remain in this state unused?”
@Audioguru, please cite your sources instead of spreading misinformation. Damage (and not quote unquote "danger", per se) _seems_ to not happen if an empty battery is recharged with low currents, according to oh about five million accounts enumerated as comments to this video [this video] .
Cites Martin Andersson · 2023-08 · Electrical Engineering Stack Exchange · on “Dead laptop batteries”
This video [this video] and all comments beneath it seems to suggest the following statement is wrong: "At 1.2V your batteries have been over-discharged, they're finished." @bobflux, can you please clarify?