3roomlab:
I have no problem to believe that. It sounds like a good practice.
I have read all about increased wear at higher SoC. Ten years ago. And ten years ago, I even designed a simple microcontroller circuit to autonomously drain li ion cells to about 3.85V for longterm storage. I built a couple of these pcbs... using the Sharpie method! There's a blast from the past. I even stored these carefully titrated cells in the fridge. I also stored some fully charged cells, and years later the float voltage on these fully charged cells was still 4.15+V. Crude testing didn't reveal anything significant. This is no surprise, to me now, because...
The li ion cells that I have been actively using for ten years, kept at room temp, and kept fully charged at 4.2V most of the time, (and also charged "improperly" using CC CV without end of charge termination), are still fine, let alone the cells that were prepped for storage in various conditions. So for me, it is not worth the bother to worry. I went thru all that initial trouble because the predominant misinformation at the time was even without being used, at all, a battery might only last 3 years!!!
It's not that accelerated death at higher SoC is't necessarily real, nor really important in certain scenarios. I just feel like for me personally, at room temperature, it is not significant. In a higher temperature application, it could be a very significant problem. Or the 30%/90% scheme could be a matter of practicality to eliminate any potential of under/overcharge in a high-S, rapid cycling application. I woudln't know. In a stand alone 1S charger, I don't see the potential for a significant problem, unless maybe it's done in a hi temperature environment. It's a one shot deal, not a high frequency hi heat application, in itself. And you will never leave a cell plugged in, indefinitely, which may occur in a laptop being left plugged in 24/7 for years. You will take it out the battery, eventually, to use it or to charge other batteries.
10 years ago, I read all this stuff, and at the time it sounded very important and official and intimidating. Maybe in another 5 or ten years, some of you will be of the same inclination as I.
By now, I have used 3-4 different li ion charging IC's in my projects. I made up some proper chargers for use with USB ports, which are within arms reach as we speak. And I still use a lab power supply more often than any "proper" charging solution when I'm at my bench, because I simply do not care, anymore. It works the same - for me. I set it and leave the battery connected without any care, probably until the next time I need it or the PSU.
AFAIC, li ion batteries last as long as I will ever care about when used properly. And CV CC charging without termination is fine and proper AFAIC. They last so long, they are essentially the death of the rechargeable replacement battery market. I learned that in most cases it was easier to simply hardwire the battery into the project and add a recharging port, rather than to have a user-replaceable, externally charged setup. This hard-wired setup is increasingly common in the consumer market.
In 10 years, 95% of batteries I have replaced were obviously damaged by human error. Summation of damage: Mostly in applications where I did not install a low voltage cutout, esp in circuitry where I did not install low current sleep modes and forgot to charge them periodically. Other batteries I damaged when I got a cheap lab supply where the voltage started to drift, then went back to my own DIY PSU. And when I finally got my latest lab supply, I didn't realize it drained the load when you turned the supply off, and I damaged another battery I had to replace (weird feeling, because it had been years since I had to do this).
Li ion batteries can easily exceed the product life cycle of many of the products they are powering, several times over. So when the battery on my Kindle dies in 6 months, I know it is because some compromises were made.
If you are careful in your own designs/usage, you may find the same thing. Some of these considerations are critical and some aren't. You may find out that some things which you thought were important are really not what is making the difference.
If you think you need to jump through a bunch of hoops in order to use a li ion battery, it's because that's what the industry wants you to think. It is child's play.
I'm not simply guessing in the dark or flying by the seat of my pants. Back in the day, I took this li ion voodoo as seriously as anyone! Here's my first battery de-charger. Sharpie, mechanical relay, linear regulators... Good grief! This probably took me 3 weeks to make! If I found this circuit to actually be of any use, I would redo it today in a quarter the pcb, in one afternoon.... and it would probably run on a li ion battery!
Haha, look at the LM339 quad comparator. I only needed 1, so cut it in half!