High-voltage batteries in electric and hybrid vehicles must be able to resist water and humidity. Unlike conventional electronic equipment, these systems combine high energy concentration with sensitive chemical materials, amplifying the risks related to water exposure. This issue is all the more critical as these batteries are often installed under the vehicle floor, directly exposing them to road spray and flooding.
These two aspects apply to all types of batteries regardless of their chemistry (NMC, LFP, solid, etc.).
Let’s talk more specifically about high-voltage batteries found in electric vehicles. These present the additional difficulty of often being in humid environments. They are also often placed under the vehicle floor, which means they can be completely submerged in case of flooding.
Standards
A strict regulatory framework governs the protection of battery packs :
- Vehicle homologation : ECE R100
- Functional safety : ISO 26262
- Transport and storage : UN38.3
- Industrial safety : IEC 62619
- Water protection : ISO 20653, ISO 6469-3
Two types of requirements and tests are required:
- Ensure that the electrical insulation of a battery is not reduced in a high humidity environment
- Ensure a sufficient sealing level for the battery pack
These standards have evolved over time and requirements have been strengthened. In particular, the evolution of the ISO 6469-3 standard was updated in 2021 :
- Tightening of tests in humid environments
Transition from an 8h / 23°C / 90% RH test → 48h / 23°C / 93% RH / insulation > 100 Ω/V - Clarification of the required sealing level: IP67, which corresponds to a battery that can be immersed for 30 minutes in 1 meter of water.
Before this date, the required tests were more similar to an IP54 sealing level, i.e., protection against water spray.
Work on these standards is still ongoing and should further strengthen protections. It is particularly the sealing that will need to be reinforced to respond to the multiplication of cases of flooding of electrified vehicles.
Technical Difficulties
Water and humidity resistance involves the use of costly technical solutions. It is estimated that bringing a battery pack into IP67 compliance represents 15 to 18% of the total battery pack price.
Except in special cases, no equipment is perfectly airtight and watertight by design. Indeed, a housing must at least be able to “breathe” in order to align the internal air pressure with the external atmospheric pressure.
Otherwise, seals and mechanical connections undergo forces that reduce their operation or gradually deteriorate them. This is why a battery pack integrates “valves” that ensure air passage between the inside and outside while ensuring liquid tightness.
The battery pack is also made up of assembled heterogeneous elements: metal or aluminum shells and covers, plastic connectors, metal anchor points, plastic cooling tubing, etc.
To ensure sealing, seals or deposits of sealing materials are used.
Finally, to fight against possible water infiltration or condensation, humidity absorption or evacuation systems are implemented.
All of these elements ensure at least the sealing level and humidity resistance required at the production date. They do not necessarily allow going well beyond these standards and ensuring their function in extreme cases. Furthermore, as reported by the American SAE analysis in 2024 , these elements can lose some of their performance over time.
Poor mechanical assembly during pack construction can also be detrimental, which is why today a sealing test by pressurization is mandatory for each manufactured battery pack.
Which risks ?
In normal situations, the risks related to batteries in humid environments are very low. Some recent studies also demonstrate that electric vehicles behave better in flooded areas than thermal vehicles.
Nevertheless, there remain situations where the integrity of the battery pack can be called into question:
- A vehicle/battery that has been immersed for several days, particularly in seawater
- A vehicle/battery stored in a humid environment and subjected to strong temperature variations generating condensation
- A physically degraded battery no longer presenting the sufficient sealing level
Unfortunately, the risks related to this type of problem can be insidious because the degradation due to these conditions can appear with delay.
Experience feedback shows that 3-5% of batteries exposed to prolonged immersion (>48h) present delayed failures, justifying quarantine protocols of at least 72 hours after exposure.