2 "stars" for the reproduced sound really too low

The big problem with this Acer smartphone Z4 remains too low sound (alarm mode even worse on maximum volume position tends to vibrate the shell according to the rings)
by dint of wanting to reduce the thickness of smartphones, there is little room in the unit to accommodate one of his mini sytem satisfactory.
Ditto for the battery which will also be reduced in size and thickness to fit the design of the device.
More design is reduced in thickness, the more fragile for use ... Electronic gear manufacturers are well aware; ultimately they gain as they reduce the quantities of raw materials for manufacturing, without lowering the prices of their devices)
The miniaturization of electronic devices of this kind is absolutely not one sign of quality or durability.

good points:
- 400x800 screen bright enough good quality, very decent for the price of the phone (Acer entry)
- Wide choice of ringtones
- Several animated wallpapers, choice of 3 colors for the icons above etc ...
- 2 micro SIM cards
- Start fast enough

negative points:
- Sound system
- Little weak battery 1 capacity: 1630 mAh (1 bit just to power all functions of the phone)
- Heating the hull up and receiving phone calls.
- FM radio mode unstable reception
- No backlight 3 touch buttons at the bottom