Most (all?) modern phones manage charging speed based on battery health, charge state, and temperature. I'm not sure you could force one to charge faster at e.g. 2% charge in 120 degree heat with any kind of cable. Mabye? But that seems like a software thing.
> Limiting max charge, on the other hand, has known strong effects.
Yes, and you used to be able to do that on a rooted android phone. But, Google required the removal of debugfs in recent android versions, so need to run a custom kernel too now to get back that functionality.
Maximum charge, and percent charge where charging begins should be user accessible settings on any device with a lithium ion battery. Charging rate should also be a user accessible setting. The cable idea is just a hacky work-around for crappy software, that addresses one of the reasons lithium ion batteries prematurely fail, and doesn't require modifying the device to be charged.
Well if you do it every time at like 2-3C, you’re talking maybe 500 cycles compared to 1000 cycles at a slower charge rate. Depends on other stuff, too. Depth of discharge and max charge voltage are both even larger effects, but it still matters. (Knowing the exact chemistry of your phone’s battery can make a difference here, of course.) https://www.mpoweruk.com/life.htm
Fast charging from, say, 10% to 50% probably is a fairly small effect compared to trying to fast charge to 100%.
Even that much is aching for more numbers. How about .5C versus 1.5C? What if my phone is one of those fancy ones rated for 6C or even 10C? Unless someone gives some precise scenarios it's so hard to guess how my phone might be affected.
