What happens to a battery after it stops holding a charge

This is less a set of instructions about battery recycling than an argument, and it is worth saying so at the start.

A dead battery is not an empty one

A device stops working when the pack can no longer hold its voltage under load, which happens long before the cell is empty. The remaining energy is more than sufficient to heat a shorted cell to the point where its contents ignite. This is why discarded cells cause fires in refuse vehicles and sorting halls, where they are crushed alongside everything else.

Damage during collection is the trigger, since a punctured cell can short internally and enter thermal runaway within seconds. Taping the terminals of loose cells before disposal removes the most common external short and costs nothing at all.

Collection is the real bottleneck

Recovery processes work reasonably well; the difficulty is that most exhausted cells never reach a facility that can process them. Small batteries embedded in cheap devices are frequently discarded with general refuse because removing them is impractical.

Mechanically, many households store old devices for years, so a large stock of material is neither in use nor available for recovery. Reported recovery rates vary enormously between countries and are measured inconsistently, which makes comparison unreliable. Any improvement in recovery therefore depends far more on logistics and design than on any advance in chemistry.

Sorting is harder than it looks

Cells arrive in mixed chemistries, and different chemistries require different processing and pose different hazards. External labelling is inconsistent and often illegible after use, so automated sorting relies on shape, weight and imaging.

The short version: packs contain adhesives, plastics, copper, aluminium and electronics, all of which must be separated before recovery. Cells glued into a device rather than fastened must be prised out, which risks the puncture that starts a fire. Designs using standard fasteners and clear labelling make the whole downstream process cheaper, and that decision is made years earlier.

Two routes to recovering the metals

One route smelts the material at high temperature, burning off the organic components and recovering metals from the molten mixture. It is robust and handles mixed input, but it consumes a great deal of energy and loses lighter elements to the slag.

The other route shreds cells into a fine mixture, often called black mass, and dissolves the metals using chemical solutions. That approach recovers more of the material and at higher purity, while producing liquid waste streams that need their own treatment.

Facilities increasingly combine the two, using mechanical processing first and chemistry to separate what the shredding produced.

A second life before recycling

A pack retired from a vehicle may retain a large share of its original capacity, which is inadequate for driving and fine for storage. Reusing such packs for stationary storage extracts more service from material that has already been mined and manufactured.

In practice, the obstacle is assessment, because measuring the remaining health of a used pack reliably takes time and equipment. Mixed packs of uncertain history are difficult to combine safely, since the weakest cell governs the behaviour of the group. Second life delays recycling rather than replacing it, so the material still has to be recovered eventually.

Design decides how much is recoverable

Adhesive holding a cell into a chassis makes removal slow and dangerous, and slow removal makes recovery uneconomic. Packs that mix chemistries or bond cells permanently into modules cannot be separated without destroying them. Marking chemistry clearly on the cell, in a form that survives use, makes automated sorting substantially more accurate.

Under load, several jurisdictions are moving towards rules requiring removable batteries and recycled content, and the details differ considerably. None of this is visible when a device is bought, which is why the decisions that govern recovery are made entirely upstream.

The takeaway

The recycling problem is mostly a collection problem wearing a chemistry costume.

Understanding the failure mode tells you more than the feature list does.