A few additional comments on my lightful behalf:
I have been dealing with and experimenting with standard li-ion cells for quite a long time now, and concerning the BU-808 li-ion battery care information provided in Battery University all I can say in a nutshell or in summary is that it absolutely works.
The magic voltage figure to maximize li-ion cells' lifespan is 3.92 V (for 4.2 Vmax cells), which in terms of proportions or ratio it is 14:15.
I installed a new quality battery cell in my smartphone in june 2019 (bought it second hand, and soon noticed that its previous user gave a very bad treatment to the stock battery), and have been using dedicated software to limit its state of charge to a maximum of 65%, and even to set a hard limit to its charge voltage and current. Smartphone batteries are high voltage types, and I limit my 4.4 Vmax smartphone battery voltage to 4.106Ģ V -14/15-). I use my smartphone quite a bit and its battery still has excellent health. I like my stuff to last for ages. O:)
Comparatively speaking, the battery of my very old laptop always lived in a full state of charge or at maximum voltage, as I didn't know better many years ago, and anyway there was no proper software to limit battery voltage or state of charge in anyway. For this reason the health of its battery deteriorated very quickly. I don't know how other people is doing in this matter with laptops, but my guess is that overall they would say that laptop battery life sucks.
What has been said concerning maximum voltage and cycle life only applies to the usual 4.2+ V li-ion batteries: Li-Co, Li-Mn, Li-NMC and Li-NCA. It does not apply to LFP (lithium iron phosphate or LiFePO4) or LTO (lithium-titanate).
No, its not the same with other ārechargeable batteriesā or battery chemistries.
Please seriously consider adding the option to fully select the battery charge voltage, fully. With this I mean that if I want 3.92 V, let me choose it, and if I want 3.45 V, let me choose it; whatever! This way you satisfy all customers, no matter if they want 4 V, 3.92 V, or whatever as I say.
I also have to say that automatic charging current selection sucks, because the charger does not know battery capacity and also cannot measure battery internal resistance properly (because no 4-wire measurement in the slots). So, manual charging current selection is usually best. You could for example start with a more or less āsafe for most cellsā current value, like 500 mA, and cycle upwards through a few selectable values: 500, 1000, 2000, 3000, 50, 125 and 250 mA. This list has 7 values, the same your S4+ charger has, but with a 50 mA value which could be handy for tiny cells like 10180s or when there's no hurry at all.
And never trickle charge li-ion cells after charging is finished. In fact, removing all trickle charge routines after charging is done is the best you can do, whether for li-ion cells or for Ni-MH. DON'T trickle charge! :| Consumers want devices which makes their lifes easier. For example, I may want or it may happen that I leave my cells in the charger for days, weeks, months or whatever, without having to worry if I left the charger powered on or off. For this reason, absolutely minimize any cell drain in the slots (your S4+ will discharge small cells in a few weeks), don't drain the cells in the slots below 2 V (I don't know if this happens in your chargers right now, but I say it just in case), and don't trickle charge.
Because moving the cell or charger at all can cause it to disconnect/reset. So you donāt dare touch anything or rotate a cell to look at the label, for example. This needs a redesign! (Old ni-cd chargers from 50 yrs ago had the exact same stamped-steel, slide/spring design. :D) Also, that would make for more reliable accurate voltage measurements.
