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$50 Prius Spare Battery - Page 2

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Posted by Bob & Holly Wilson on October 29, 2007, 2:11 am

I'm not selling either of my batteries. However, they come up on Ebay
from time to time.

Huntsville Alabama.

The battery pack consists of 38, cell packs with six, 6.5 Ah cells in
series. NiMH cells at full charge are at 1.2. Each cell pack is at 7.2
VDC at full charge for 273.6 VDC.

The process I'll use is as follows:

1) use a 300-400 W load to discharge the battery to an average voltage
of 0.9-1 VDC, ~228 VDC and cutoff at that level
2) measure open cell pack voltage for each pack
3) using a constant current, ~1A., to recharget the battery pack to 275
3a) monitor the cell pack temperatures and look for hot packs
4) remove the charger and let cells sit for an hour and normalize their
5) put a 300-400 W load on the battery assembly and measure the
individual cell pack voltages during the discharge to ~228 VDC

Based upon these measurements, I should have a mapping of the strongest
and weakest cell packs. I have four spare battery packs and will weigh
the weakest and spare packs and put the heaviest ones back in the pack.
I'll also shift the strongest cell packs into the location of the
weakest cells. Then I'll repeat the whole pack test.

When done, the strongest cells will be where the weakest cells were
removed. The weakest cell packs will be removed for electrolyte
refreshing.  Then I'll recharge the pack and install the two, high power
sockets and safety relays.

When I'm done, my 2003 Prius will have a battery pack with a plug-in
tickle charger. This means every morning I'll start the car with a fully
charged battery, actually I'm shooting for 78-79% state of charge as
well as a warmed engine and transaxle.

The current pack will then go through a survey to identify the strongest
and weakest cells. Again, the weakest cell pack assemblies will be
removed and the strongest cell packs shifted to put the strongest ones
where the weakest ones were located. Then I have this spare inverter I'm
planning to use with the battery pack for home power.

Bob Wilson

Posted by mrv@kluge.net on October 29, 2007, 3:40 pm
On Oct 28, 10:11 pm, bwilson4...@hotmail.com (Bob & Holly Wilson)

And just where are the ticklish spots on your Prius?  I don't think I
want to know your testing methods to get your Prius to giggle.


Thanks for bringing back Prius discussion to the
alt.autos.toyota.prius list!  8)

Posted by mrv@kluge.net on October 29, 2007, 3:50 pm
 On Oct 28, 10:11 pm, bwilson4...@hotmail.com (Bob & Holly Wilson)

Just be aware of the hybrid battery repacking/recharging problems that
the owners of the MKI original Japanese 1998-2000 NHW10 Prius owners
are having outside of Japan...  Yes, an out-of-pack recharging
technique has been developed, as has the "Frankensteining" of more
than one bad battery packs (rearranging the cells/modules).  However,
one cannot just take all of the strongest modules and string them
together - that'll still give a battery fault.  All of the modules
have to be "matched" such that they all have about the same output.
The recharger info is in the files section, and there's been much
discussion about the NHW10 battery repair techniques and trials at

(This older cylindrical battery design is far less robust than the
prismatic design in the NHW11 or NHW20 Prius sold internationally.
With the right paperwork and repair history, within Japan, Toyota is
doing free swapouts of these older battery packs when they get their
permanent turtle lights and battery fault indicators.  Outside of
Japan, owners are out of luck...)

Hopefully you won't run into any similar problems when rebuilding your
NHW11 batteries!  (At least it is easier for you to come across old/
used battery packs, as compared to the out-of-Japan NHW10 owners!)

Posted by Bob & Holly Wilson on October 30, 2007, 1:02 pm

Thanks for the heads up but I am taking a cautious approach. One 'lesson
learned' from some of the EV community is the prismatic batteries need
mechanical limits on expansion. I don't know if this due to excessive
charging current generating gas, heat or other characteristics. In the
meanwhile, I am thinking about getting a load-cell to measure the

Bob Wilson

Posted by Wayne on November 1, 2007, 2:13 am

What does that mean?  You can't actually dismantle a cell and change the
chemical pastes inside, can you?

  Then I'll recharge the pack and install the two, high power

How many "batteries" are in the car?
Do you buy replacement cells, or packs?
Where do you buy them?
How much to they cost?


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