Trevi FLEX 50 GS Guide De L'utilisateur page 29

3. Insert the battery by paying attention to the metal contacts.
4. Replace the rear cover carefully, taking care not to damage the
plastic anchors.
5. Before using the unit for the first time, you must fully charge the
battery to use the USB cable and power supply.
Note:
• If the battery is fully charged, the phone will not turn on, it will
take 4 minutes to allow the phone to reach a sufficient charge state
for startup.
• When the battery is low, the unit will emit a sound if the charge is
insufficient, the unit will turn off automatically
WARNINGS ON SIM CARDS
The SIM card slot is designed to accommodate only the SIM of the
corresponding fee. The use of Micro or Dual SIM with its adapter
is not recommended as it may cause damage to the device and the
Micro/Nano SIM itself.