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Old Battery ?

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Posted by Stephen G. Giannoni on February 3, 2015, 7:26 pm
I have a 2001 with 64K miles with the original HV battery (14 years
old !) How long do these typically last? Is it a function of both time
and service? So far it's performing as always. What would be the first
signs of aging, etc.?

Posted by bwilson4web on February 4, 2015, 11:43 am

On Tuesday, February 3, 2015 at 1:26:11 PM UTC-6, Stephen G. Giannoni wrote

The failure mechanism is the electrolyte dries out. The terminal seals of t
he 38 battery modules have a rubber "O" ring to seal in the small amount of
 gas that forms in normal charging. But when the battery gets hot, the "O"  
rings let a little of H and O out and over time, this dries out the e
lectrolyte. Hot climates with little shade and hilly terrain driven at high
 speeds heats the battery modules to higher temperatures. So some will fail
 sooner than others, usually the ones in the middle of the pack where it is
 most difficult to keep them cool.

The next generation battery modules have improved terminal seals and more i
nternal, cell-to-cell connections to reduce resistance. The 2004-09 modules
 were a substantial improvement and the 2010-current even better.  

If you have a Prius-aware scanner, one that can read the battery module-pai
r voltages, you can get an idea of how well the pack is balanced. There is  
also a procedure described in Volume I of the shop manuals about how to tes
t the pack.

When modules in the pack are ready to fail, they lose their amp-hour capaci
ty. So the pack appears to charge very fast and discharge very fast. Eventu
ally a cell within a module will short out and then you'll get an error lig
ht and a Prius-aware scanner can identify the failed module. This is anywhe
re from a week to a month before the pack fails where the car no longer run

We've written fairly detailed descriptions about this over in the PriusChat
 forum as well as the Yahoo Group, "Prius Technical Stuff." Both have much  
better archives with PriusChat dating from 2004 and "Prius Technical Stuff"
 from 2001.

Bob Wilson

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