How far can LiIon be discharged? This sticky covers battery voltage and sag pretty thoroughly. You can also follow two links near the end of the original post. There’s not much capacity left below 3.4 volts. Most cell phones shut down at about 3.3v or even higher. And yes many cell phones charge up to 4.3v or even 4.35v. The Samsung flagship phones and others including iPhone do give you the option to charge to 85% capacity. They do that to extend the batteries useful life.