Exact backup time depends on how active the device is (.i.e. How much current the device is drawing during standby vs alarm condition).
VoiceAlert old versions compatible
Mega will provide you with 5-days of backup
This is required if you use Solar power. The reason is that a security solution can never afford to be without power. The combo of a 10w solar and 5-day battery means that even in the darkest weeks of winter, a single day of scattered sunlight will get your battery fully topped up