jdm cars are not built for long life, its against their economy as they produce a lot of cars and they NEED to sell them. That is why the paint is so cheap on them too.
these sort of shields are used a lot in EU, US, Africa, ME, Russia etc in cars where the battery is installed in the engine bay, e.g the Ford Focus etc have a full battery box with dedicated vent in the engine room. old BMW had a jacket type button down cover for batteries like Volvo, SAAB etc. - In those two it was specified to keep the battery warm as it also had a heater patch on it too.