Lithium-Ion Batteries in Tools, Vans and Customer Equipment

Why this matters

A modern service shop carries dozens of lithium-ion packs, charges them in places nobody designed for charging, and meets more of them in customers' garages every year. A healthy pack is boring. A damaged one can sit quietly for a day and then go into a fire that a garden hose does not stop, in a van parked next to the house or in the back of a garbage truck after somebody tossed it. The shop that knows the signs, charges deliberately and has one recycling route avoids almost all of that for the cost of a shelf and a roll of tape.

What thermal runaway actually is

A lithium-ion cell is a sandwich: a graphite anode, a metal-oxide or phosphate cathode, a separator (a polymer film a fraction of the thickness of a sheet of paper) between them, all soaked in an organic electrolyte that is flammable. The separator is the only thing keeping the two electrodes from shorting.

Thermal runaway is the chain that starts when it fails. An internal short heats a small spot, the heat melts more separator, the short widens, the electrolyte starts to decompose and give off gas, and in the common metal-oxide chemistries the cathode releases oxygen of its own, so the cell feeds its own fire. The cell vents, often with a hiss or a pop, then a jet of white or gray smoke that is itself flammable, then flame. In a pack, one cell's heat drives its neighbors into the same chain one after another, which is why a tool pack fire comes in surges rather than one burst.

Three things follow from the mechanism, and they drive everything in this card:

• The fire carries its own oxygen, so smothering it with a blanket or a lid does not reliably stop it. Fire services generally fight it with large amounts of water for cooling, and a cell that looks out can reignite as the next one goes.
• The smoke is toxic, not just irritating. Vented electrolyte releases hydrogen fluoride among other gases. Nobody stands in the smoke to deal with a burning pack.
• Damage and fire can be hours or days apart. A crushed or punctured cell may sit at room temperature until the internal short finally bridges. A pack that "seemed fine after the drop" is not cleared by having seemed fine.

Lithium iron phosphate cells, common in newer storage and some tool lines, are more thermally stable and release far less oxygen, but they still vent flammable gas. Treat chemistry as a reason a pack fails less often, never as a reason a damaged one is safe.

What starts it: four causes

Physical damage. A fall onto concrete, a pack run over, a screw driven into one, a crushed corner. The internal layers deform even when the housing barely shows it.

Charging outside the cell's temperature window. Charging a cell below freezing plates metallic lithium onto the anode, which grows into fine spikes that can pierce the separator later. A common cell specification allows charging roughly between 0 C and 45 C (32 F and 113 F); your tool maker's manual states the window for its packs, and most quality chargers refuse a pack that is too hot or too cold. A cheap charger that does not is the danger.

Overcharge and the wrong charger. The battery management circuit and the matched charger together stop a cell at its full voltage. A knock-off charger, a damaged charger, or an adapter that bypasses the pack's electronics removes that stop.

Age and abuse heat. Repeated heavy draws, storage in a hot cab, and simply years of cycles degrade the separator and the electrolyte. This rarely causes a fire by itself; it shortens the pack's life and narrows the margin for the other three.

The damaged-battery signs

A pack is treated as damaged, and handled under the damaged-battery procedure rather than ordinary recycling, if it shows any of these:

• Swelling. A bulged housing, a pack that no longer slides cleanly into the tool or charger, a phone or tablet whose screen is lifting. Swelling is gas inside the cell, and it means the chain has already started at a low rate.
• Heat without use. Warm to the touch when it has been sitting.
• Hiss, crackle, or a sweet solvent smell. That is electrolyte vapor leaving the cell.
• Leaking, staining or crusting around the seams or terminals.
• A cracked or punctured housing, or a pack that rattles after a drop.
• Smoke or scorch marks, however faint, on the pack or the charger.
• A charger fault indication on that pack and no other, repeated on a known-good charger.

Hand any of these to the procedure. See related: The Damaged Lithium Battery Handling SOP. A pack that simply holds little charge, with no physical sign, is end-of-life rather than damaged, and goes to ordinary battery recycling.

Charging and storage in the van

The van is where shops take the most risk without thinking about it, because it is where charging is most convenient.

Charge in the shop, not the parked van, as the default. A closed van in summer sun can run cargo-area temperatures well past the top of a typical charging window, and an inverter running overnight in a locked vehicle is a charging fire with nobody present to see the first smoke. The common starting policy is: packs charge on a non-combustible shelf at the shop, on the tool maker's own chargers, during working hours or on a timer, with nothing stacked around them.

If a van must charge, it charges while somebody is driving or working beside it, on a properly installed inverter, with the charger secured so it cannot slide, and never in the cab.

Let a hot pack rest before charging. A pack straight off a long cut is often at the top of its window. Fifteen minutes on the shelf costs nothing; most good chargers will hold it until it cools anyway.

Store spares loose, not in a pile. Packs on a shelf or in their tool case. Never loose in a metal bin with screws, bits or other batteries, where a bridged terminal is a dead short.

In winter, a pack that spent the night at freezing warms to room temperature before it goes on the charger.

Customer equipment: what you will meet and what you owe

E-bike and scooter packs charging in garages, robotic mowers, cordless yard equipment, battery-backed openers, and installed home energy storage. Also lithium metal cells, which are not rechargeable: the sealed long-life batteries in smoke alarms, many remotes and sensors. Different chemistry, same rule about the trash, because a crushed lithium metal cell burns too.

The tech's duty here is mostly to notice and to say. A swollen e-bike pack on a charger next to the water heater is the customer's property and the customer's decision, but a tech who walks past it has missed the one thing on the call that could burn the house down. Unplug nothing that is hot or hissing; tell the customer what you saw, where it is, and that it needs to come off the charger and out of the house to a battery recycler.

Taking it away is a choice, not a duty. If the shop takes a customer's damaged pack, it takes on handling and transport under the damaged-battery procedure and the shop's own recycling route. Installed energy storage systems are their own trade with their own listings and fire code requirements; a tech who is not trained on that equipment documents and refers rather than opening it.

Why "just the trash" is how trucks and plants burn

A lithium pack in a dumpster, a garbage truck or a recycling bin meets exactly the conditions that cause runaway: compaction crushes it, and the surrounding paper and plastic is fuel. Waste haulers and recycling facilities report fires from batteries routinely, and EPA published an analysis of these fires in 2021. A recycling bin is not a battery route either; curbside programs do not take lithium batteries and a pack in a sorting line is the same hazard one step later. No lithium battery of any kind goes in the shop dumpster, the curbside bin or a customer's trash. See related: The Dumpster Fire From a Battery in the Trash.

Recycling routes

Federally, used lithium-ion and lithium metal batteries can be managed as universal waste under 40 CFR Part 273, which keeps them out of the shop's hazardous waste count when handled that way; the duties are in the owner card. See related: Universal Waste Explained for a Service Shop. In practice a shop uses one of three routes: a retail or manufacturer take-back program for intact rechargeable tool packs, an electronics or battery recycler under contract, or a county drop-off that accepts business batteries. Most retail drop-off programs do not accept damaged batteries, so the damaged ones need a recycler that explicitly takes them and tells you how to pack them.

Prepare intact packs the same way every time: tape both terminals with non-conductive tape or bag each pack individually, then store them in a plastic or fiber container, not a metal one. Shipping batteries to a recycler by carrier is regulated under the DOT hazardous materials rules at 49 CFR 173.185, which has separate packaging requirements for batteries sent for recycling and for damaged or defective ones; the recycler or carrier specifies the packaging. Carrying packs in your own van is a transport question. See related: Hazardous Materials in the Service Van.

Worked example: a six-tech shop audits its packs

A six-tech plumbing and electrical shop runs one tool platform. Each van carries six packs and the shop holds six spares, so 6 x 6 + 6 = 42 packs. After a pack swelled in a charger, the owner pulls all 42 onto the bench on a Friday afternoon and sorts them against the signs above.

• 34 healthy. No swelling, cool, seat cleanly, charge normally.
• 5 end-of-life, intact. Each holds a fraction of its rated runtime but shows no physical sign. Terminals taped, boxed in a fiber carton, routed to the tool maker's take-back program.
• 2 swollen. One will not seat in the tool at all. Both go to the damaged-battery procedure.
• 1 cracked housing. Dropped from a ladder two weeks ago, works fine, not warm. Treated as damaged anyway, because the crack proves an impact the cells also took, and two weeks without a fire clears nothing.

That is 34 + 5 + 2 + 1 = 42, every pack accounted for. 3 of the 42, about 7 percent, needed the damaged-battery route.

The reasoning behind the hard call: the owner's first instinct was to keep the cracked pack in service because it works. Working is not the test, because the damaged-battery signs describe the cell's condition and the tool's performance describes nothing about the separator. One cracked pack in a 42-pack fleet is cheap to replace and expensive to have go up in a van.

The audit then turned up the cause of the original swelling. Two techs were charging packs overnight on van inverters during a hot spell, in vans parked in full sun. The shop moved all charging to a steel shelf in the shop on a timer, with a written rule: no charging in a parked, unattended van.

What would have changed the answer. On a platform where packs were inexpensive and swapped constantly, the shop might simply retire any dropped pack on sight rather than inspect it. A shop with one pack per tool and no spares would feel the cracked-pack call much harder, which is the argument for carrying spares. And a shop whose county drop-off refuses business batteries has no route at all until it signs up with a recycler, which is the thing to find out before the bin fills.

The failure mode. The common one is the pack that swells, gets set aside "for later" in the back of a van with loose screws, and is forgotten until it vents.

How to verify you have it right

Pick any van at random and check four things: no pack on a charger in the parked van; spare packs in a case or rack, terminals not touching metal; no swollen or cracked pack anywhere in it; and the tech can name where a damaged pack goes. Then check the shop: a taped-and-boxed container of end-of-life packs with a date on it, and a recycler's name on the wall that accepts damaged batteries.

References

• EPA, An Analysis of Lithium-ion Battery Fires in Waste Management and Recycling (2021)
• 40 CFR Part 273, universal waste batteries; 49 CFR 173.185, lithium battery transport
• Tool and battery manufacturer documentation for charging temperature windows
• See related: The Damaged Lithium Battery Handling SOP
• See related: Universal Waste Explained for a Service Shop