As far as I know, it has always been advised that slow charging is the best for battery longevity, and I can't see any evidence for that changing.
Nothing in life is perfect, so the designers have to settle for acceptable compromise backed up with a warranty.
Having bricks of parallel connected cells is fundamental to Tesla's current battery design and while they have gone to great lengths to control and monitor what goes on outside the bricks, it would be difficult to monitor each cell within every brick.
This is basic stuff, so any tech will be yawning, but just for focus here now -
Three things being monitored at a brick level are
1) current through the brick
2) voltage across brick (must be same for all cells because they are in parallel. That's pretty much a definition of parallel connection)
3) the cells do NOT have the same current flowing through them. (that is pretty much the other definition of parallel. There are parallel pathways for current to flow which is why small cells are connected that way to sum their individual current capacities)
The problem I see is that while you can measure the voltage for all cells in a brick (since its the same for all) you can't measure current without adding a super low value resistor in series with each cell and measure the volts dropped across those resistors to give you current through each cell.
Internal resistance of each cell already dissipates heat when cells have current flowing, so you could theoretically measure each cell temp to see how hard it is being worked' but your cooling system is working against that idea by trying it's best to keep everything at a uniform constant temperature. However, I guess that both hard-working cells and 'lazy' higher resistance cells both do the same thing under heavy load / high charge rate, but for different reasons. (both get hotter). So elevated brick temperature could signal things going out of whack in that brick. What you are really looking for is uneven heating within the brick I think.
One solution solution is pefect cell matching, but although you can get close, I don't see how you can get perfect. And keep it perfect. Not realistic or necessary.
Re manufacturing battery packs must be a very tricky black art since you would likely need a supply of pre-aged good condition bricks to replace once containing cells that have deteriorated differently.
One mitigation approach that gives you save power from a given number of cells and fewer cells wired in parallel in bricks where you can't 'get at them' is to put more bricks in series and run higher pack voltages.... like 800v designs. This presumably makes switch gear and other electronics harder to design (think running higher compression ratios in ICE) but reduces heat generated).
I think it is important to recognize that most serious engineering design is about mitigating undesirable behavior and optimizing what's desired.
May be we are just starting to appreciate some more inconvenient truths, but that's when engineers need to really earn their keep.Tesla have done incredible things. May be they over-promise. Quite a few examples of that. Sadly, my view is that this practice is so rife / prevelant that you almost can't avoid it in today's markets.
I opted for a non-performance model based on a gut feeling not very well thought through that keeping stresses low on the battery has to be a good thing. The car does everything a need and I love driving it.
