Troubleshooting Guide

 Initialize the headset to factory defaults => ref
https://helpguide.sony.net/mdr/wfsp700n/v1/en/contents/TP0001613432.html
 Make sure that the headset is set on the charging case securely.
 Check that you are using the micro-USB cable supplied.
 Check that the micro-USB cable is connected to the charging case and the computer firmly.
 Make sure that the USB AC adaptor is firmly connected to the AC outlet.
 Check that the computer is turned on.
 Check that the computer is not in standby, sleep or hibernation mode.
 Charging may not be successful depending on the USB AC adaptor.
 If not used for a long time, the duration of the rechargeable battery may be shortened.
However, the battery life will improve after a few recharges.
 If you store the headset for a long time, charge the battery to its full capacity once every 6
months to avoid over-discharge.
 If the headset is not used for a long time, it may take longer to charge the battery.
 If the computer enters into hibernation mode while connected to the headset, charging will not
be completed properly. Check the setting of the computer before charging. The indicator (red)
will go off automatically if the computer enters into hibernation mode. In this case, charge the
headset again.
 If the headset or charging case detects a problem while charging due to following causes, the
indicator (red) may turn off or flash although charging is not complete. In this case, charge
again within the charging temperature range. If the problem persists, consult your nearest Sony
dealer.
 It is recommended to charge in a place with an ambient temperature between 15 °C and 35 °C
(59 °F - 95 °F). Efficient charging may not be possible beyond this range.
 If the headset is not used for a long time, the indicator (red) may not light up when you
connect the micro-USB cable to charge the headset. Wait for a specified amount of time until the
indicator (red) lights up.
 If the life of the built-in rechargeable battery drops significantly, the battery should be
replaced. Consult your nearest Sony dealer for replacement of the rechargeable battery.
 Avoid exposure to temperature extremes, direct sunlight, moisture, sand, dust or electrical
shock. Never leave the headset in a parked car.
 When connecting to a computer, use the supplied micro-USB cable only, and be sure to
connect them directly. Charging will not be completed properly by an indirect connection, such
as via a USB hub.