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This is a question related to What makes primary batteries leak on very deep discharge?

What are the dangers of deep discharging a cell or battery? I've seen a LiPo battery getting puffy most likely because of deep discharge, so I'm curious if there are safe cells. E.g. does a 0 V NiMh cell pose a danger? I'm aware that you most likely destroy your secondary cell by discharging it really deeply.

Are there safe or unsafe battery or cell technologies, either primary or secondary, in respect of deep discharging? Can a circuit without battery protection mechanisms like a joule thief make cells pop, heat, or burn?

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  • \$\begingroup\$ I deep discharge my INDIVIDUAL Energizer Ni-MH batteries for each discharge. Then they do not become polarity reversed. Many Lithium rechargeable batteries have a "protection" IC in them. The products my Li-PO batteries are used in do not work when the voltage becomes low so the batteries are never deeply discharged. \$\endgroup\$
    – Audioguru
    Commented May 4, 2023 at 15:06

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It depends on the battery chemistry. NiCd or NiMH batteries will permanently fail if discharged too far through a process called polarity reversal. Sometimes this can be partially corrected by running a large charging current (~10-30C) for a few seconds, but this isn't without its dangers. However, the good news is that your battery is basically a paperweight...I haven't heard of any self-destructing in any way so dramatic as to take less than a year.

Li-ion batteries, though, will undergo electrolyte decomposition, producing gas. While hard-walled batteries will usually contain this pressure (or in the case of microdefects, bleed it out gradually) LiPos will swell noticeably, and could potentially rupture. The good news here is that the battery is deeply discharged, and doesn't have the chemical energy left for a huge flameout. You're likely to get away with just a small fire and the release of multiple poisonous substances.

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Can a circuit without battery protection mechanisms like a joule thief make cells pop, heat, or burn?

For alkaline batteries, I have seen them leak, pop, and corrode. Most electronics will only bring alkaline cells down to 0.8V per cell, but a Joule-thief can bring battery voltage down to especially low levels -- down to 0.5V and even lower -- where I have found these problems to be worsened and made more frequent, especially the leaking of corrosive alkaline fluid, which easily destroys battery contacts and circuit boards.

Lithium-ion batteries are infamous for "exploding" (or I think I remember the term "rapid disassembly", which was used as legal double-speak to downplay an event more comparable to a roman candle, or a shower of sparks firework).

I recommend against using a Joule-thief with unprotected Lithium-ion cells unless you really know what you are doing (you have the necessary qualifications). Even then, you might want to use a dutch oven or other fireproof container.

Are there safe battery or cell technologies, either primary or secondary, in respect to deep discharging?

The good news is that there is a technology very similar to a battery called a supercapacitor, which can be safely discharged all the way down to zero without repercussion. They don't hold a whole lot of energy (a one night Joule-thief is possible, try this supercap, 450 F (EDLC) Supercapacitor 3 V Radial, Can - Snap-In - 4 Lead 3.6mOhm, $12.32 as of May 4, 2023), and will have to be frequently recharged, as it now stands. But we have high hopes for this technology, that it will soon advance to the point of being more comparable to conventional batteries.

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