Lithium-Ion batteries maintain pretty much full discharge rates right up until they have reached the "Maximum Number" of Charge/Discharge cycles....
and then, they just poop out...
One more thing to be aware of, Lithium-Ion batteries like to be kept in the upper 2/3rds of their charge status.... so, Caveat Emptor if you insist on always running them down flat between charges. That is a guaranteed way to kill them prematurely.
The manufacturers recommend that we use 40% as the bottom of the discharge cycle, and top it off from there. I have "tried to" observe that recommendation, and I have yet to ever replace a Lithium-Ion battery in any of my smartphones. If, you observe this method, it greatly extends that "Maximum Number" of recharge cycles.
I have still working:
1 each - Samsung Galaxy S purchased eons ago when it first came out, still working just fine, gets put back into service spasmodically on emergencies.
2 each; Samsung Galaxy S5 phones, both working great
1 each; S Note 4 and working great
1 each HTC One M9 about a year old, no issues at all with it.
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Verizon: Note 4, two ea. Galaxy S5, HTC One M9, VZW MiFi
MyPhoneExplorer lets you access a broken phone while locked
Nova Prime, Textra, Aqua Mail, Qi wireless equipped
MacroDroid can help extend battery life
MacroDroid senses Screen off, turns Wifi OFF
MacroDroid senses Screen UnLock, turns WiFi ON
PureVPN when using a public WiFi