IamIan said:
Myself I'd be ok with anything less than about ~50mV of balancing.
Well, partially true.

Nope .. sorry to break it to you .. but you're wrong .. not partial at all .. it is 100% true that I'd be ok in the context here with anything less than about ~50mV of balancing .. and what I am ok with is 100% up to me to decide
It depends on the cell chemistry if we are speaking about 50 mv.
This context doesn't have multiple different chemistries .. it as one battery Peter put together of A123 AMP20M1HD-A cells .. but even if it did .. it would be more accurate to write something like .. It would depend for you .. because only I get to decide what I'd be ok with .. and if I choose to be ok with less than ~50mV , that is what I've chosen .. I don't get to chose what you would be ok with anymore than you get to decide what I'd be ok with.
A123 cells, which I believe retepsnikrep is using is pretty huge because of the very flat discharge curve. Just image balancing a123 cells with 50 mv, it would be pretty bad.
Yes he is using A123 20Ah pouch cells AMP20M1HD-A.
I disagree with your conclusion .. I don't think it would be pretty bad .. not even bad at all .. if balanced to less than about ~50mV , I'd be ok with it (in a 5-95 use window).
The toshiba LTO cells, its like .02 volts is an amp hour. so 50 mv would be about 2.5 amp hour of capacity.
I'm skeptical of this claim.
Even assuming you are referring to the modules form the Fit people are using.
None of the tests I've done or seen of the Toshiba SCiB LTO cells show the ends (where it matters in this context) of a cell charge or discharge being linear like that .. so using linear logic there is questionable .. the ends top and bottom are far more exponential than linear .. the ends matter in this context , because it is the ends where a cell gets over charged or over discharged.
Under your linear logic of 50mV ~2.5Ah .. that would mean from 1.900v to 2.600v .. which is still in the OEM usable range .. aka a 700mV difference , those Toshiba SCiB LTO Fit cells would give 35Ah in that range .. which no test I've seen of them show that .. because the ends (top and bottom) are far more exponential than linear.
I'm a little confused about what you think this graph is showing ??
Because it looks to me to be supporting what I wrote.
1st .. it's a different battery .. not the one being used in the context of my statement (AMP20M1HD-A ) .. unless you plan to use those A123 26650's to make a 12v car battery (context of this thread).
2nd .. to me .. even if you did want to use that battery .. context of this thread to make a 12v car battery .. instead of the one Peter is using (that my coment was about) .. I'd still say the same thing .. I'd be ok with anything less than about a ~50mV balance (with a use range of 5-95) .. look at the ends of that discharge graph you posted .. the point where a bad out of balance cell could hit the bottom first .. aka how much capacity is left in the last ~50mV on the bottom .. In my subjective opinion the wh/ah left in that ~50mV is a small amount of Ah / Wh .. so small that in the 5-95 window I described , I'd be ok with just being less than ~50mV , even with those 26650 LiFePO4 A123 cells in your discharge graph.
Although I myself .. I also wouldn't use just a 1p4s pack of 2.5Ah 26650 cell A123 cells like that for a 12v car battery replacement .. the ~20Ah AMP20M1HD-A cells Peter used , maybe .. 3P4S of the AMP20M1HD-A , that would be more in mine of my own personal preference .. but .. that's just me .. to each their own.