Lithium battery fires are the hazard the extinguisher range was not designed for. A cell in thermal runaway generates its own heat and its own oxidiser inside a sealed package, so smothering it does not stop it and cooling the outside only slows it. Understanding that is more useful than buying any particular cylinder.
Why a battery fire is different
Thermal runaway is a self sustaining chemical reaction inside the cell. It produces heat, flammable and toxic gases, and it propagates to neighbouring cells. An extinguisher can knock down the flames around a pack and the pack will reignite, sometimes minutes later and sometimes hours later, because the reaction inside never stopped. That is the property that makes these fires so difficult.
What a class D metal fire extinguisher covers, and what it does not
Class D is burning metals: magnesium, sodium, potassium, aluminium swarf and lithium METAL. A lithium ion battery is not lithium metal and a class D extinguisher is not the answer to one. This distinction is genuinely confusing and it is exploited in marketing. If your site holds lithium metal, you need class D powder and an applicator; if it holds batteries, that is a different problem.
What actually helps with batteries
Large quantities of water applied for a long time, which cools the pack enough to stop propagation, is what the fire service does. Some proprietary agents aimed at battery fires work on the same cooling principle and can help with a single small device. For a duty holder the effective controls are upstream: charging in a designated place, away from escape routes, on the correct charger, and not charging overnight or unattended.
Where this bites
Premises storing or charging e-bikes and e-scooters, warehouses holding battery stock, offices with charging lockers, and residential buildings where bikes are charged in corridors. In residential blocks the escape route issue is acute: a bike on fire in a communal corridor removes the only way out, which is why charging in escape routes is the thing to prohibit first, before any equipment is bought.
Questions people ask about lithium fire extinguishers
Is there a lithium extinguisher for battery fires?
Nothing reliably stops a pack in thermal runaway, because the reaction sustains itself inside the cells. Cooling with a lot of water for a long time is what the fire service does. Controls on charging matter more than equipment.
Does a class D extinguisher work on lithium ion batteries?
No. Class D is for burning metals including lithium metal, which is not the same thing as a lithium ion battery. This distinction is frequently blurred in marketing.
What should a building do about e-bike charging?
Designate a charging location away from escape routes, prohibit charging in communal corridors and stairwells, require the correct charger, and avoid unattended or overnight charging.
Does a lithium ion fire extinguisher exist?
Units are sold on that description, usually water based with an additive, and none stops the cell to cell reaction once it has started. What they can do is cool a pack and buy time, which is worth having and is not the same as putting the fire out.