Just want to bounce around an idea here.
It's based on these general "impressions" which I have gained from my 2 year peek into battery technology:
Impression A) People want more range than what the currently available batteries can provide.
Impression B) Batteries last much longer if they are being cycled in many shallow cycles, rather than frequent deep cycles.
Impression C) Batteries get damaged by heat caused by a variety of "mechanisms". The worst damage is probably done by heating up excessively from the inside out, particularly by exceeding maximal charge and/or discharge rates, and over-charging and over-discharging.
Impression D) You need high voltage batteries to keep cable sizes and resistive losses low in the overall system. More volts generally mean more "Ooomph" and more speed. Unfortunately, this also makes it very dangerous.
Impression E) To get more Ooomph you need many cells and that means a complex and expensive Battery Management System (BMS).
Impression F) Batteries generally like it to be used to no more of 50% of their capacity, for both peak current draw and total Ah drain.
Impression E) There is always one cell that bites the dust first - depending on circumstances, it may then take the others down with it...
Now to the conclusions from these impressions:
1) Combining A) + B) +F) ===> In order to get good battery-lifetime range, the available trip range needs to be reduced even further - by about 50% ! Not a popular idea, I'm quite certain...
2) Because it is always one cell that goes down first, you might as well make sure you know exactly which cell this will be. If you can be certain that this cell will be the one that gets over-charged or over-discharged before all others and that it suffers more heat damage than all other cells, then you only need to monitor this single cell! That's the idea. Quite simple.
The proposed solution (possibly hogwash!):
Place a sacrificial cell into the battery string, monitor only this cell. The operating conditions for all other cells should then always be within the parameters conducive to maximising the lifetime energy delivery of the battery.
Here is an example to illustrate the idea:
Imagine a 40s 40Ah battery.
Instead of monitoring every cell, place just one 25Ah cell into the series and monitor this cell constantly.
When it dies (and die it will!), replace it with another 25Ah cell, again and again and again, until the pack has deteriorated down to maybe 30Ah.
Once the pack capacity has deteriorated significantly, despite the very gentle treatment it is receiving, you could either get a new pack or use an even lower spec sacrificial cell to keep it going.
Needless to say, older cells of the same product line might be perfect sacrificial cells. Down-cycling at it's finest!
What say you?