Hybrid and EV batteries on a tow yard: the storage risk nobody prices in

A hybrid or EV sitting on your lot still has a charged high-voltage battery in it, whether or not the car will ever start again. If that battery is lithium-ion and it has been damaged, it can catch fire again hours or days after anyone last looked at it. The safest high-voltage pack on a tow yard is one that is no longer there.

A dead car does not mean a dead battery

Turning a hybrid off opens the relays between the pack and the rest of the car. It does not drain the pack. Toyota's emergency response guide for the second-generation Prius describes a 201-volt nickel-metal hydride pack, made of 28 modules in series, which the car's system boosts to as much as 500 volts. Power stays in that high-voltage system for 5 minutes after the pack is shut off.

That is the ordinary case: an intact Toyota pack in a car that simply stopped running. The orange cables are the visible part of it, and they are orange for a reason.

What the NTSB found at tow and impound yards

In 2020 the National Transportation Safety Board published a safety report on lithium-ion battery fires in electric vehicles. It names tow operators as "second responders", the people who deal with the car after the fire department leaves, and several of its findings happened on yards.

• Batteries reignited after the fire was out. The damaged batteries the NTSB investigated "reignited multiple times, even days after a crash."
• One reignited on the impound yard, twice. An SUV from a crash in Mountain View, California, started popping about 20 minutes after it was unloaded at an impound yard, then reignited. It caught fire again five days after the crash, under a tarp.
• One damaged its neighbours. The report describes a Chevrolet Volt that reignited three weeks after a crash test and damaged four nearby vehicles.
• The recommended spacing did not fit. The NFPA and vehicle manufacturers recommend a 50-foot clear area around a stored, damaged EV. At the Mountain View impound yard there was not enough room, and the NTSB concluded that a 50-foot radius "may be infeasible at tow or storage yards." With more than one such car on a lot, it said, the space would "most likely be impossible."

That is the liability in one sentence. A damaged EV can light itself hours or days later, and most yards cannot give it the space the guidance calls for.

Nickel-metal hydride is a different risk, not no risk

Most Toyota and Lexus hybrids, and older Honda hybrids, use nickel-metal hydride packs. Plug-in hybrids and EVs use lithium-ion. Every fire and reignition case in the NTSB report involved lithium-ion. If you want the longer version of the difference, it is in our post on NiMH vs lithium hybrid batteries.

A nickel-metal hydride pack is still around 200 volts. Toyota's guide describes its electrolyte as an alkaline of potassium and sodium hydroxide. It is held as a gel and will not normally leak, but crushing or cutting a module is not "normally". Treat it as a shock hazard and a chemical hazard, even where it is not the fire hazard a lithium pack is.

What to do with the ones you are holding

• Keep damaged EVs and plug-ins apart. Use distance where you have it. The NTSB report cites SAE J2990's alternative where you do not: a barrier of earth, steel, concrete or solid masonry around the vehicle.
• Do not park them nose-to-tail with other cars. The Volt case is what happens when a pack reignites next to other vehicles.
• Watch the ones that have been in a fire or a hard crash. The Mountain View SUV started with popping noises. Smoke, hissing or popping from under a car means calling the fire department, not investigating.
• Keep people off the battery area. Standing on, cutting into or stacking anything over the floor of a damaged EV is flexing the part you least want flexed.
• Do not cut orange cables. Pulling a pack is a job for someone trained and equipped for high voltage, not a job to learn on.
• Do not crush or shred a car with the pack inside. That is a big enough subject to have its own post: why the pack comes out before the crusher.

Getting the packs off your lot

The simplest way to stop storing a risk is to stop storing it. In the Phoenix metro we buy hybrid packs that are worth rebuilding, because every rebuilt pack we sell is made from modules that came out of another one. Anything we cannot use goes to a licensed recycler. Collection is free, with no minimum, and there is paperwork for every pack that leaves, so you can show where it went.

Tell us before collection if a car has been in a crash, fire or flood, and whether the pack is still in it. Damaged packs are handled differently, and we will tell you straight away whether we can take one.

Details for yards and shops are on our trade core page, or call 623-323-0737 and tell us roughly what you have on the lot.