Car surveillance project - Intelligent phone charger communicating over USB

hello,

     i working on car surveillance project use android phone central processing unit.
     this topic focuses on how maintain phone powered on, no matter use car daily or not use weeks. have in mind is:
     hw:
        1.  have android phone hidden somewhere in car
        2.  have attiny85 device
             - powered on battery of car
             - connected usb external port of android device
             - connected car signal informing when engine on/off
             - having transistor or relay being able provide 1a @ 5v phone, through usb connector
      sw:
        1. android phone runs custom application written b4a that:
             - communicates on usb attiny device. attiny seen cdc device
             - monitors level of phone battery , sends message attiny when level goes under defined threshold or when gets 100%
         2. attiny runs arduino sketch that:
             - when engine on, charges android phone no matter battery level reported
             - when engine off, starts charging android phone when message received on usb level under threshold , stops charging when android says it's full
 
        question have is: phone accept powered attiny device, giving fact run usb host , attiny usb device? in configuration guess phone want power device rather being powered it, not sure.

      thank in advance.
         

any idea ? 

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