Most lithium-ion incidents in UK workplaces do not happen while a battery is sitting on a shelf. They happen while it is on charge, or in the hours immediately afterwards. Charging is when a cell is being pushed hardest, when a manufacturing defect or earlier impact damage is most likely to show itself, and — because charging usually happens overnight or over a weekend — when nobody is there to notice.
This guide covers how to charge lithium-ion batteries safely in a workplace: where to do it, what rules to write down, how to handle damaged cells, and what a fire-rated charging cabinet actually adds. It is a practical summary written by a supplier of storage equipment, not legal advice — your own fire risk assessment and DSEAR assessment take precedence.
Why charging is the risky moment
A lithium-ion cell that is overcharged, physically damaged, internally short-circuited or charged outside its temperature range can enter thermal runaway: an internal reaction that generates its own heat faster than the cell can shed it. Once it starts, it is effectively self-sustaining. Cells vent flammable, toxic gas, and a pack containing many cells can propagate from one cell to the next.
Two consequences follow for how you set up a charging area. First, separation matters more than suppression — keeping a failing battery away from other batteries and combustibles limits the event. Second, you cannot rely on someone spotting it, because the majority of charging happens out of hours.
What UK duties apply
There is no single regulation titled "lithium battery charging". Several existing duties combine:
- Health and Safety at Work etc. Act 1974 — the general duty to provide a safe place and safe systems of work.
- The Regulatory Reform (Fire Safety) Order 2005 (England and Wales; broadly equivalent regimes apply in Scotland and Northern Ireland) — the responsible person must assess and manage fire risk, which now clearly includes battery charging.
- DSEAR 2002 — where charging can release flammable gas or create an explosive atmosphere, the risk must be assessed and controlled.
- PUWER 1998 — chargers and battery-powered equipment are work equipment: suitable for purpose, maintained, and used by trained people.
In practice, the deliverable is the same in every case: a written assessment that names where charging happens, what could go wrong, and what you have done about it.
Where to charge: siting the area
Most of the risk reduction comes from location, and it is free. Aim for a charging point that is:
- Away from escape routes. Never charge in a corridor, stairwell, lobby or doorway that people need to get out through. This is the single most common finding on fire risk assessments.
- Away from combustibles. Cardboard, packaging, pallets, aerosols, solvents and gas cylinders should not share the space. Keep chemicals in proper hazardous storage.
- On a hard, non-combustible surface, not on carpet, wood or a pile of stock.
- Ventilated and temperature-stable. Manufacturers quote a charging temperature range — often narrower than the discharge range. Charging a very cold or very hot battery is a genuine failure mode, so avoid unheated outbuildings in winter and direct sun in summer.
- Covered by detection. Smoke or heat detection in the charging area, tied into the building system, buys you the warning that an unattended charge otherwise removes.
The charging rules worth writing down
- Use the charger supplied for that battery. Universal and third-party chargers are behind a large share of workplace incidents. Match charger to pack, every time.
- Never charge a damaged, swollen, dented, punctured or water-damaged battery — or one that has been dropped hard, even if it looks fine. Quarantine it instead.
- Do not cover the battery or charger while charging, and do not stack packs on top of each other.
- Disconnect when charged. Leaving packs on charge indefinitely keeps them at maximum state of charge, which is the least stable place for a lithium cell to sit.
- Avoid charging at 100% as routine. The widely used 40–80 rule — keeping cells roughly between 40% and 80% for storage and topping up rather than running flat — is primarily a longevity practice, but it also reduces the time a pack spends fully charged.
- Let hot batteries cool first. A pack that has just come off a hard shift or out of a fast-discharging tool should reach room temperature before it goes on charge.
- Log it. A simple charging log makes it obvious when a pack is ageing, running hot or taking longer to charge — the early signals that it should be retired.
Damaged and end-of-life batteries
Damaged cells need somewhere to go that is not the charging area and not the general waste. Set aside a quarantine point — ideally outside, away from the building, in a non-combustible container — and make it someone's job to arrange collection by a licensed waste carrier. A swollen pack in a desk drawer "until someone deals with it" is how a lot of incidents start. A damaged pack should never go back into a charging cabinet, so keep a separate sealed, non-combustible container for it.
What a fire-rated charging cabinet adds
A charging cabinet does not stop a battery failing. What it does is contain the consequences and buy time — which is the whole point when the failure happens at 3am. The asecos ION-LINE range we supply is built around that logic:
- Type 90 to EN 14470-1 and 90 minutes to EN 1363-1, the standards used for fire-resisting safety storage cabinets, covering a fire outside and a fire inside.
- Insulated, propagation-tested shelves on the full-height cabinets to slow spread from one pack to the next.
- A bottom collecting sump on the full-height cabinets (1 litre on the ION-CORE-90, 2.6 litres on the ION-PRO-90) for leaks — the same containment principle as our spill containment range.
- A transport base so a damaged cabinet can be moved with forks, plus lockable doors; the ION-PRO-90 has self-closing doors with 3-point locking.
The three cabinets are an under-bench ION-CORE-90 (eight UK sockets, two drawers), a full-height ION-CORE-90 (four shelves, sixteen sockets) and the ION-PRO-90 (six shelves at 75 kg each, forty-eight sockets, VDMA 24994 certified). Size by power and pack count: count the packs on charge at once, and remember asecos' manual states technical ventilation is required on the full-height ION-CORE-90. Full specifications sit on our lithium battery storage range, and our companion guide covers what UK guidance expects of a storage cabinet.
Two related cases are worth separating out. Charging laptops, tablets and phones for staff or students is a different job, handled by ventilated device charging lockers rather than fire-rated chemical cabinets. And the lithium packs on powered pallet trucks are charged in place under the manufacturer's instructions, in a designated bay — not in a cabinet.
Turning it into a procedure
A workable charging procedure fits on one page: where charging is permitted (and where it is banned), which chargers may be used, the pre-charge visual check, the rule on damaged packs, who to tell if something is hot or swollen, and what to do if a battery starts venting. Add signage at the charging point, brief it to everyone who charges anything, and review it when you buy new equipment. Fire response in particular should come from your fire risk assessor — lithium fires behave differently from ordinary combustible fires, and the right answer depends on your building, not on a supplier's blog.
FAQ
What is the safest way to charge lithium batteries?
Use the manufacturer's charger, on a hard non-combustible surface, in a ventilated area away from escape routes and combustibles, at room temperature, with the battery visually checked first and disconnected once charged. For workplace quantities, do it inside a fire-rated charging cabinet with smoke detection in the room.
Can lithium batteries catch fire when not being charged?
Yes. Thermal runaway can be triggered by physical damage, an internal manufacturing defect, or heat — none of which require the battery to be connected. This is why damaged packs need quarantining and why storage cabinets exist as well as charging cabinets.
What is the 40–80 rule for lithium batteries?
It is the practice of keeping lithium-ion cells roughly between 40% and 80% state of charge rather than routinely running them flat or holding them at 100%. It is mainly about extending cell life, but it also reduces the time a pack spends at full charge, which is its least stable state.
Where is the safest place to charge a lithium battery at work?
A dedicated, signed charging point on a non-combustible surface, away from escape routes, stock and flammables, within smoke or heat detection coverage — and, where quantities justify it, inside a fire-rated cabinet. An unheated outbuilding is not a good substitute: charging outside the specified temperature range is itself a failure mode.
Do I legally need a lithium battery charging cabinet?
No regulation names one. But the Fire Safety Order and DSEAR require you to assess and control the risk, and for anything beyond a couple of small packs a fire-rated cabinet is usually the most straightforward way to demonstrate you have. See our guides on COSHH cabinet requirements and flammable versus COSHH cabinets for how the same reasoning applies to chemicals.