I'm new to this discussion list, so I ask your patience: my understanding of
EV systems and Li-ion batteries is limited.

The question is: replace a bad battery in a pack of 19, or make the pack 2
batteries smaller and suffer an unknown loss of voltage and range?

Background:
  
I think I have a bad battery in one of 19 batteries that is in the second
bank of a 4 bank x 19 CALB CA40FI battery pack.  The battery pack is used in
a 10KW battery that is part of a Plug-In Supply conversion of a 2004 Prius
to a plug-in Prius.  Robb Protheroe installed the system in late 2014, and
it has seen about 10K miles, maybe 60% of that in all electric mode, about
900 partial or full charge cycles.  

The evidence that the battery is bad is an incomplete loop circuit.  I found
that the battery management board atop the suspect battery was not powered,
and moving that BMS board to another battery adjacent powered it.    The
suspect battery was at 2.67V.  The others adjacent are at 3.0V.  Originally
they were all balanced at 3.26-3.27V. 

Robb Protheroe at Plug-In Supply suggested replacing the battery with a new
one.  Unfortunately CALB no longer makes this 40Ah battery, but the Sinopoly
or Winston 40Ah prismatic cells are nearly the same dimensions and
specifications.  It looks like I can get a replacement for about USD$60 
including shipping to me in Maryland USA, using www.ev-power.eu (a US
supplier wanted $42 shipping for a $55 cell).  

The other option is to remove the bad battery and the one adjacent, and
carry on with a lower voltage pack.  Robb is unsure whether the range loss
would be proportional (7%, I can live with that), or more, due to "voltage
sag" and age of cells.  He suggested I ask you, so here I am.

Questions:

1. Would you recommend replacing or removing batteries from my pack?

2. If removing, what is your guess on loss of range due to lower pack V,
voltage sag?

3. If replacing, do you expect the new cell to assume the lifetime of the
rest of the batteries in the pack, as others have written on this listserv?

So far I am thinking to try removing, see how the range is affected by
testing on a known route that is longer than the original hybrid range with
this pack installed.  If unacceptably worse, add back the replacement cell. 
If not, carry on with the slightly smaller battery pack.  But I would be
grateful for the wisdom of the list.

Thank you in advance for your help,
Mike



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