today I found something I looked for since quite a while: cheap notebook style chargers with customizeable end-of-charge voltage: http://www.groetech.de/index.php?main_page=index&cPath=5&zenid=ogh3dl0iql13c2edc1hn83jep1
the description is in german and basically says for most of those charger: there is a poti inside, that allows you to fine tune the end-of-charge voltage which is AWESOME for batteries without a bms.
you notice how the cells working interval appears to be probably around 3.3-4.0V, i.e. the small tip from 4.0 -> 4.2V doesnt hold too much capacity and below a certain voltage (probably really around 3.2-3.3V), the voltage also drops really fast (again not too much capacity in that area).
now reducing your end-of-charge voltage has a 2-fold effect: firstly youll be able to prolong your battery life without much downside really -> quoting batteryuniversity: most Li-ions charge to 4.20V/cell, and every reduction in peak charge voltage of 0.10V/cell is said to double the cycle life. For example, a lithium-ion cell charged to 4.20V/cell typically delivers 300–500 cycles. If charged to only 4.10V/cell, the life can be prolonged to 600–1,000 cycles; 4.0V/cell should deliver 1,200–2,000 and 3.90V/cell should provide 2,400–4,000 cycles.
and secondly (and the reason why Im so keen on it): it allows you to essentially run without a BMS for a long time, because even though cells might or might not drift: the headroom for a drifting cell to reach a value beyond 4.2V or below 2.5V is quite large in a safe custom interval like 3.3-4.0V!
and you get these 2 things without much of a downside really - just some capacity loss, which, if you look at the plot, isnt a really big deal. sure, if you got very small batteries like 200Wh and less, you probably cant really afford lower end-of-charge, but people with 400Wh+ should consider it imo!