Traction Battery Lifespan

My 2003 is now approaching 120,000 miles with no apparent problems with the major drive elements throughout the vehicle's life. After reading about the cost of replacing the traction battery, I am concerned about its lifespan. Is there any data/opinion of the usable life of the battery? I read several threads about the condition of the battery relating to the charge status indicator (consistant low charge meaning the battery is no longer effectively charging). Is there any reliable indication (battery charge bar/error codes, etc.) that the battery is beginning to fail or is nearing the end of its useful life? Or is this a sudden death situation?

There aren't many good options:

• Ask service center to read out module voltages - fairly straight forward, you look for a significant voltage drop in one module, more than 0.3 V but this really isn't a measure of the pack health.
• Discharge/Charge voltage measurement - more involved, Art's Automotive has a web page about the process that involves monitoring the minimum and maximum module voltages while forcing the traction battery to discharge and then recharge. Sad to say, we can get a relative measure but not an absolute 'life' gauge.
• Force charge to maximum and backup a hill - this provides an absolute measure of how much energy the traction battery held ... but it is rough on the battery.

There have been a fairly small number of traction battery failures but they seem to be associated with hills and hot weather. Descending hills heats the battery and hot weather also raises the temperature. With enough heat, it looks like the NHW11 modules develop small leaks at a terminal and after losing enough water, a cell, one of six in a module, fails. But this leads to plenty of warnings. There is no 'time' but rather usage that seems to accelerate traction battery failure.

So far, it looks like between salvage vehicles and Toyota replacements, the NHW11s remain on the road. The most recent experiment of replacing NHW11 modules with NHW20 modules appears to be working very well. Here are some of my experiments.

FYI, our NHW11 has 121k miles.

Bob Wilson

when mine dies, i will let you know how long it lasted... hope u a patient person

Kenopa, I say forget about the HV battery for now, and get the transaxle fluid changed and that pan cleaned out.