I recently had a bottle of water leak in my back seat of 2006 Toyota Highlander. Then all of a sudden car would start. I had just taken water proof dog seat cover off to clean seats the week before and hadn't replace yet. Go figure. When I had to have car towed in Toyota they check out and said water damaged to Hybrid battery and my Toyota Extended Coverage and Hybrid Warranty isn't valid to cover repairs. I contacted Toyota in Calif and they confirmed. Service manager said something about a cover/fix that Toyota had made. Has anyone else had this problem. What else can I do? This is a traversity, They tell me $975 for relay might fix issue but if not $7000 to replace battery. Why wasn't there any warning not to have liquids in back seat( which I didn't even know that was were battery was) 2) if Toyota has made a fix for this issue wouldn't that be considered a design flaw and that they should cover this? Please desperate for any assistance...

 

Same thing with my 2007 highlander. This is ridiculous. Waithing for call back from toyota.

 

When you open up the battery case (under rear seats) there are 4 main components; traction batteries, Hybrid ECU, Hybrid relay and the wiring harness. Water (or any liquids for that matter) on the traction batteries should not damage them at all (they are very robust, no way to harm them), but there is a drain at the bottom and all the liquids spilled are supposed to drain out harmlessly. Issue is that this drain often gets plugged with junk that falls down behind the seats and forms a plug (there's an updated part that fixes this issue). When this happens often the Hybrid ECU ($750 list) or Hybrid relay ($250 list) gets fried (liquids can ground out the wiring harness) and one or the other needs to be replaced. They are not cheap but itīs alot less than buying a complete new battery ($5000 list). The traction battery modules will never be damaged in such a scenario so if a dealer tells you otherwise I suggest changing service locations until you get someone more competent.

Here's some good info on the same subject:
http://futureforecast.com/blog/?p=522