Although the device has several features and algorithms to save battery consumption so it can last for 15 hours or more, there are however a number of factors that can make the device consume more power:
Movement - By default, the device will save energy if it is stationary and not moving. Once it detects movement, it will continuously update its location every few minutes and will consume more power.
Signal - The device uses GSM signal both for communication and data. A lost or weak signal of GSM will force the device to constantly attempt to connect and consume more power.
Voice Call/Voice Message - Constantly using the device for Voice Calls, and Voice messages can also consume more power.
Location Log Frequency - By default, the Lilo Watch attempts to update its location every 1 minute. You can change the Location Log Frequency in the settings (How?)
Loose Charging cable - it could be that the charging cable was not properly inserted and the watch was charging intermittently.
We highly recommend that you charge the device at least 4 hours daily to make sure the battery is always full.