Hybrid Car – More Fun with Less Gas

User rebuilt battery

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Posted by Bob & Holly Wilson on January 6, 2008, 5:58 pm
Hi folks,

As a refreshing change of pace, there are two known examples of NHW11,
2001-03, battery packs being rebuilt. The first is in Europe by Florian
Steiper in Germany and a collaborative effort between Eric and myself:


The photo is my battery assembly reconditioning unit using an MRC 989
and two custom built end plates. When an NiMH battery charges, it can
generate gas if over charged. One of my end-plates has a capacitance
load cell that at 13.3 nF is only under clamp pressure, not gas

I have three spare cells and will pickup an additional 36 cells for
refurbishment the end of this month. At $0-40 each, this means a failed
battery pack can have just the failed cells replaced and get back on the
road again.

Both battery repairs occurred in Nov-Dec so it is too soon to know how
long they will last. But for now, two NHW11 Prius have been returned to
service for a lot less than a complete battery pack replacement.

Comments? Questions? Concerns?

Bob Wilson

Posted by notaguru on January 7, 2008, 12:59 am
I'm impressed. A few times in my distant past it became
necessary to identify and replace a bad cell in a
high-voltage series set, and it rarely worked as well as
the original. That was probably due to careful matching.

It will be great if you provide more information as time
goes on...


Posted by Bob & Holly Wilson on January 7, 2008, 3:19 am


What I did was ship the battery fully charged, this means above the
standard 80% limit. The instruction to the user was to discharge the
cell assembly until the no-load voltage matched that the of the adjact

Normally, our Prius battery packs wander between 40-80% but sit mostly
at about 60%. This means there is 'head room' so imperfections between
the cell assemblies seldom leads to  over/under charge conditions.

But battery assemblies that run closer to 100% down to 0% are especially
sensitive to balanced cells. In fact, it would be nearly impossible to
achieve long battery life if all of the cells has to match at these
extreme charge ranges.

Bob Wilson

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