Allow instant boot after phone with empty battery is connected to power Let's say my phone is out of battery, and has turned itself off. I get to a charger, and connect it. Maybe I need to make an urgent call. But my phone refuses to boot until the battery is at 5%. It only takes like ten minutes to get to 5%, but still, I'd like to remove this limitation.

Some phones (and other devices) can even boot without the battery as long as they are plugged in, so I don't reckon it should be technically impossible to boot my phone with an empty battery if it's plugged in. The phone should be able to power itself from the charger alone, if nothing else.

My charger gives plenty of power, enough to use heavily and still charge at the same time.

I reckon the reason they have created this limitation is because if the user then unplugs the phone while the battery is at 1% or something, the phone may not have sufficient time to shut itself down properly. But I'm aware of that danger, and I  still want to have control of this myself.

Is it possible to remove this limitation of 5% battery before boot?

To clarify, when I'm using the phone (and it's not plugged in), it goes all the way down to 0% without automatically shutting down. So there doesn't seem to be any limitation there. But if I then connect it again, that's the limitation I'm talking about. I then have to wait until it gets up to 5% before I can boot.

My phone is an Asus Zenfone 2 running Lollipop. It's rooted and I have Xposed Framework.
tl:dr Mobile devices unlike laptops are not designed to run off the charger, without a battery (there are exceptions of some devices, way back).  A fully discharged battery is as good as no battery, so connecting to charger will not power up the device. Unless the battery is charged to a minimum level, it cannot be used to power the device


A battery is said to be discharged when it reaches 3V level ( also called deep discharge) . At this voltage 95% of the energy is spent , hence the mobile is designed to power down before it reaches this level
Battery charging has different stages with corresponding voltage levels as shown in figure below. The current fed from charger in the initial stages is very low (trickle charging , represented by 0.1 C, where is the Charging rate- see figure). It is only after the battery is charged above 3V, it can function. This accounts for the time it takes to charge to 5% and be able to power up the device (Not sure of the exact voltage level)





Additional factors that come in play for not permitting battery to operate before 5% :


There is a safety margin that is built in , since deep discharge followed by full charge (3.9 V) 
would cause undue stress and is not recommended 
Powering up a mobile from switched off state requires significant power (you would typically see at least 1 to 2% drop). If the battery voltage falls to below 3V due to this load, your battery would again shut down
Increasing charging rate (to reach level required for battery to operate) is a physical hazard, as the battery may explode



To sum it up, Li Ion or Li PO batteries have a bunch of physical security needs to be met. This combined with battery longevity and performance considerations, safeguards need to be in place - shutting down at low battery % , allowing the battery to reach required voltage levels is a part of the big picture. Understandably, given the mobile device penetration , nobody would like to cut corners (despite that one hears batteries exploding, recently in news)