what to do if iphone A1429 is dead, black screen, will not charge, computer doesn't see devise

My daughters iphone apple 5 A 1429 is dead. It will not charge, black screen, and my laptop doesn't see device when attached via an approved usb cable. I have attempted to charge device using different cables and different power sources. She stated it failed to charge and only brought it to me months after the battery had lost all power. I have only a rudimentary knowledge of device but serviced computer until my retirement. Shouldn't the phone show some indication upon plunging it in to a usb port or will a very bad battery prevent the charging screen to appear and the laptop from seeing any device. I have cleaned power port with canned air and measured 5 volts at the plug. I considered replacing the battery but didn't as I believe that if that was the only problem my laptop would attempt to configure the device or the charging screen would light up. But I have seen phones that a very bad battery would pull the voltage down so low the device appeared dead in the water. I don't know what my next step should be. I can find no information telling how an apple iphone will react to a dead battery. I.m sure in her attempt to fix the problem she either left the phone on the charger for days or left the power switch on for months when she was unable to charge the device so this is not like a normal repair when the device was working a few days ago and the battery has some life in it even if its will below the needs of the phone.

I wish to attempt the repair myself even if I fail as I find it amazing to service a device so small. Its sometime difficult to recall how big the computers were I serviced when I was first in the business, The processing power of an iphone ounce required huge computers that needed clean air conditioned rooms with raised floors just to handle all the connecting cables. Any help you can provide would be appreciated.

Matthew Smith