Nowadays, most modern phones use Lithium Polymer (Li-Po) batteries. Lithium Polymer batteries don’t need to be charged before the first use, because (if the manufacturer that sold you your phone wanted) they will probably already be charged to about 60-70%.
The thing is, Li-Po batteries wear down. That is, they lose the capacity to hold charge slowly over time. This wear happens whether you use them or not, though it happens faster with use. The most optimal situation for most batteries, in which this wear happens the slowest, is at a slightly refrigerated temperature, at a charge level of about 60-70%.
This is not really a problem for consumers: You can’t store your phone in the fridge, and permanently keeping it charged to 70% probably isn’t very feasible either.
For companies that deal with large volumes of Li-Po batteries that will not be used while in storage, it can however be a good idea to charge those batteries to 60-70%, since storing them at lower or higher charge levels can adversely impact the life expectancy of the battery.
Therefore, when you receive your new smartphone in the mail, it will nowadays usually be charged to about 65% and ready to use. There is no real need to charge the phone before use, but 60% is of course not even 2/3 charged.
It would probably be wise to charge the phone whilst configuring it, so you won’t run out of power later on the day. You are likely sitting still while you are configuring it anyway…
No. You do not need to fully charge ANY battery to the max until usage. It does not matter if it’s new, old, a phone, or even a remote. It does not affect the battery unless that battery has been over-used. So, what I am saying is, no. You do not need to fully charge something new before usage.
Most of the time, yes you have to charge the phone fully and then sometimes fully discharge it the first time you use it. Most of the time you’ll be fine with the phone turned on while you charge it the first time, as long as it gets fully charged before unplugging it.
There are a few reasons for this, some historical, some practical. The historical reason is that with older battery tech, the battery had to go through a full charge/discharge cycle in order to keep the battery life high.
Phones would be shipped with batteries that only had enough power in them for initial set-up, forcing the owner to do a full charge when they got home.
The practical reason is that batteries don’t maintain their charge indefinitely when they’re unplugged, so although your phone may have been shipped with a battery that started off with a full charge, by the time it gets to you, it may already be very low.