I’ve managed to get a few old mobile phones back to life using this method.
Edit: as a safety note this is not recommended! Please read some of the comments below!
Lithium battery charge circuits generally have a fully charged voltage (about 4.2v), a fully discharged voltage (about 3.2v), and a 'do not attempt to recharge below this' voltage (about 2.4v).
The reason circuits are designed not to recharge a cell below the 2.4v threshold is because when you recharge below that voltage, gasses are typically generated which eventually (many months later usually) burst the plastic envelope of the battery, and the battery electrolyte then evaporates as a highly flammable gas, killing the battery and potentially starting a fire if there is a nearby ignition source.
TL:DR:. 'dead' batteries refuse to charge for safety reasons, and tricks to bypass that safety mechanism might lead to a fire a few months down the line.
[1] Forgot it was there and put some stuff down on it - there's now about a 20° degree bend in the middle of the long side that goes about half way across the back. Somehow, the screen didn't break.