Respraying your hybrid or EV? Understand the max temperature limit for high voltage batteries

As electrified (xEVs) vehicles become more common, after-market vehicle repair shops must also adapt to the requirements of battery-powered cars. Batteries don’t like high temperatures, but baking a new coat of paint in an oven is a necessary step for many collision repair jobs. It is also not realistic to expect paint shops to remove the high voltage traction battery from the car. Bridging this disconnect between paint repair processes and battery health is tricky.

There is a strong correlation between battery health and exposure to high temperatures. This is why it is important to ensure that cooling vents and fans at the back hybrids (HEVs) are well maintained and for BEVs, coolant piping for the battery are regularly inspected.

Without going too much into chemistry, the simple explanation on why high temperature harms batteries is that all matter is made up of atoms and molecules that are always in motion. Heat is a form of energy and when heat is applied, the erratic movements of these atomic particles and molecules become greater, and therefore more chemical reactions result from the materials within the battery’s cells, resulting in accelerated degradation.

In normal driving conditions, your hybrid or BEV’s battery is more than capable of dealing with even the hottest weather conditions. It is safe to say that you will collapse from heat first before your hybrid or BEV's battery starts throwing up an error code.

The problem, however, is that temperatures inside a spray paint booth can reach 80 degrees Celsius, which is beyond the operating range of any high voltage traction battery. Since the vehicle must be disabled during repairs, the car's battery cooling system is not operational, and this is when extreme heat becomes a problem.

All manufacturers of hybrids and BEVs have their own guidelines for high temperature 'force dry' paint curing. Usually the recommendation is to keep it below 60 degrees Celsius, for no more than 45 minutes.

According to vehicle collision repair support website I-Car, Tesla’s body repair manuals for the Model S and Model X states:

“It is acceptable to “bake” (force dry) the vehicle in a paint booth with the HV battery installed as long as neither of the following parameters are exceeded:

Maximum baking time: 45 minutes.

Maximum baking temperature: 165° F (74° C).

Maximum HV battery temperature during baking: 60° C (140° F)”

It's a similar guideline for hybrids. If you look at the front door frame of newer Honda hybrids like the Civic RS e:HEV and HR-V RS e:HEV, there is a warning label that says maximum temperature of 65° C.

We’ve checked with Honda Malaysia and they confirmed that all authorised Honda service centres with body and paint repair facilities have the equipment to comply with this requirement.

They also added that this 65° C limit also applies to earlier i-DCD (City Hybrid, Jazz Hybrid, HR-V Hybrid) and IMA (Insight, second generation Jazz Hybrid, FD and FB generation Civic Hybrid) models.

Not all manufacturers put a caution label like Honda, but it is safe to say that this precaution applies to all hybrids and fully electric vehicles.

With a lower curing temperature, the painting process will of course take longer to complete, which will in turn result in higher repair cost.

Anyway, curing temperatures need not be as high in Malaysia, because of our hotter ambient temperature.

Well known independent auto body and paint shop Poon Auto in OUG – the only after-market auto body painter in Selangor equipped to apply environmentally-friendly ‘gloosy wet look’ water-based paint - explained that guidelines published for overseas markets must be put in context of their lower ambient temperatures.

“Due to our hotter climate, paint curing temperature is actually lower than what’s required in Europe or in the US,” said Joel Poon, a third-generation auto body and paint craftsman and a former product trainer at renowned auto body paint supplier PPG.

His family is known amongst collectors of classic cars as being one of the best in the business. Their shop is one of the few to follow manufacturer-level 4S-centre standard of tidiness, with bright overhead lighting.

Their paint booth is also one of the few independently-owned ones in Malaysia that is built with proper downdraft ventilation - with dust-free filtered air coming down from the ceiling, exiting through underground suction fans below – exactly as recommended by manufacturers to avoid overspray and fine dust. Many independent painters typically avoid costly underground digging work and settle for side wall-mounted suction fans.

Poon Auto has also done respraying work for hybrids and EVs, and he acknowledged that yes, extra care must be taken for cars with high voltage batteries.

Paint supplier PPG - which Joel used to do training for - guideline for respraying hybrids and BEVs is to use short or medium wavelength infrared (IR) lamp tubes for the paint curing process.

Joel explained that the shorter the wavelength IR method heats only to the car body’s surface, without permeating deeper into the battery or electronics inside the car.

But just as too much fast food is not good for you, the best paint jobs are the ones that are done slowly, allowing enough time for the paint and clear coat to settle down before starting the next process.

Joel is not an advocate of unnecessarily intense high temperature ‘force dry’ method to speed up work, regardless of whether the vehicle is an hybrid / EV or not.

Even Porsche Malaysia's 4S centre (and there's only one, in Johor Bahru) limits its paint booth's curing temperature to just 65 degrees, regardless of whether it's painting an electric Taycan or combustion engine 911.

The above fully analogue ‘80s classic BMW E30's paint job was done by Poon Auto. With no high voltage battery, it doesn't require specialized care but still, no high temperature curing treatment was used on this car.

After applying the first layer of paint, this E30 was left to air dry overnight inside the closed paint booth with filtered air downdraft ventilation, before starting a mild temperature curing process the next day. It's not something that you read on guidelines used overseas, but again, this is possible because of our warmer climate.

Of course, few paint shops can afford to do work this slowly – customers may not appreciate the longer time required, and the longer turnaround time also incurs more cost.

If you own a hybrid or a battery EV and require paint repair work, do check if the painter is aware of requirements for electrified vehicles. But as Joel explained, regardless of vehicle type, high temperature forced drying should not be overdone.

But if your vehicle has been involved in a bad accident, then the obvious choice would be to send the vehicle back to the manufacturer's authorised body and paint centre, why? Because few independent auto body panel beater shops are equipped to do digitized chassis alignment measurement. You get what you pay for.

Speaking of collision repairs, electrified vehicles, especially battery electric ones, are completely different from regular combustion engines. Even if the car is switched off, the high voltage electrical architecture is still active and body repairers need high voltage certification and protection gear before they can work on electric cars.

Despite so much talk about EVs being the future, only two companies in Malaysia - Bermaz Auto (Mazda, Kia, Peugeot) and Mercedes-Benz Malaysia offer apprenticeship to school leavers, equipping them with the necessary certifications to work on high voltage cars.

But the subject on lack of investment in growing local talent to support the EV shift is another topic that we will keep for another day. For now, let’s just digest on the max temperature guideline for curing paint on electrified vehicles.