This depends on many factors: operating temperature, number of locations with bad reception, but mostly on the frequency of location reports scheduled.
To give you some examples:
If your device is set to report once a day, expect to recharge it once every 3-5 month
If your device is set to report once an hour - expect to recharge it once a month
If your device is set to report once every 10 minutes - we recommend that you set different frequencies for day and night times. If you do this - expect to recharge the device once a week.