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Lexus Hybrid Unique Mystery

None of three dealers has ever encountered this problem. The hybrid battery on my 2006 Lexus RX400h, 80,000 miles, was ruined by water. It cost over$7000 to replace it. No one can figure out how the water got into the battery compartment under the back seat. They claim everything is sealed except the two air vents just off the back seat floor. I’m positive he roof hatch and windows were never left open in the rain and car is under cover 95% of the time. I’m afraid this will happen again if I don’t find the source of the water. The warrenty did not cover water damage, but my insureance did. They probably won’t pay a second time though. Any thoughts? This car has been perfect otherwise – maybe the best vehicle I’ve ever owned, so I want to keep it a long time.

Knowing where this RX400h lives might give a clue to where the water is coming from. Do you live in Seattle, Chippewa Falls, Phoenix, or Cape Hatteras. You should think about the source; inside, (AC) or outside? Rain, snow, flooded roads, car wash. And where it might leak in. Top, bottom or sides. If the car never drove through a flooded arroyo maybe you can eliminate the lower air vents. Snow packed under the car? Do you wash the car a lot? Is there any clue about how much water leaked into the battery compartment and how fast, a little over time or a lot all at once?

Remember Sherlock Holmes’ advice:
when you have eliminated the impossible, whatever remains, however improbable, must be the truth

If you have sunroof, there are drains to handle water that can get in around the seals in the sunroof. If those drains are clogged or somehow are disconnected the water can collect somewhere and the area of your problem is one of the places that water might go. I’m not sure where those air vents are located, but when air can get in so can water so I suspect them too. The heat and possible vapors from the batteries makes some air venting necessary so you can’t block the vents.

My suggestion is to take the car to a body shop, perhaps even the dealer’s body shop. Ask them to drill some drain holes in a some “low” areas in the battery compartment. That way if water gets in the area, it will have a way to drain out. If you cannot positively identify where it is coming from, assume it will happen again and find a way to handle any water that comes in by giving it a way out.

If there’s enough space in the battery compartment, I suggest going to Home Depot or Lowe’s, picking up a few of those battery-operated water alerts that are meant to be put on basement floors, and sticking those in the compartment.

Water has an amazing knack for finding manufacturing defects. I had a Honda CRX with a water leak which I eventually traced to a nearly invisible pinhole in the raingutter sealant. A dab of RTV solved the problem, but I had to remove half the trim inside the car and spend several hours “raining” on the car with a garden hose to find the pinhole.

Then I had a Toyota Tacoma that leaked, also due to defective application of sealant at the factory, and I had to do the rain test all over again.

The only way to find leaks like that is to remove interior trim in the area that’s getting wet, spray the exterior of the car with a hose for a LONG time, and keep checking the interior until you see exactly where the water droplets are coming in.

Until someone sees with his/her own two eyes exactly where the water is coming in, you’re just guessing, and you can waste a lot of time and money guessing.