Following a mobile phone charging issue I came across this intriguing discussion thread on reviving dead batteries and or devices.

It starts off with a phone but goes not to rechargeable tools (drill, chainsaws etc)

https://www.ukworkshop.co.uk/threads/how-i-charged-an-old-removable-mobile-phone-battery.146855/

I'm sure we could all learn something from this, for example DeWalt device battery terminal

It turns off permanently by design if the residual cell voltage drops below about 2.7v. The normal operating voltage is 3.2v - 4.2v. The 3.2v point is the arbitrary 'zero' point. At some point just below that, the battery is considered to have 'failed' and the circuitry disables it. If the voltage further drops below 2V, the lithium can turn metallic and form web-like structures, which can short-circuit the cell, heat up rapidly and go into thermal runaway. I've seen it twice and nothing can stop it. It's like a jet engine.

E2A: Here's the Battery University site's take on reawakening sleeping batteries:

Battery University

BU-808a: How to Awaken a Sleeping Li-ion

Li-ion batteries contain a protection circuit that shields the battery against abuse. Depending on the manufacturer, the protection circuit of a Li-ion…

Edited 3 hours ago3 hr by StringJunky