When APN is configured (also GPRS mode) which is required when using i-Server app, it automatically puts the PeTrack in an active state and it does not allow it to go to sleep naturally as it does when in SMS mode (text mode). The reporting time (in the App settings) is not going to have any influence on the battery. What might have some influence is the report time configured on the unit itself by using a set of commands.
However, please keep in mind that when the PeTrack has APN configured (or in GPRS mode) and using i-Server app it does not go to sleep, which would give you maybe 8 hours tops of battery life. If it is in SMS mode, it would give you about 6-7 days (battery life) of daily use.
There are some PeTrack users who use both GPRS and GSM mode. They have a drafted text message to activate the APN so they can use i-Server app for maybe an hour or two. Then, turn i-Server app off and send the command to remove/disable the APN to the unit to allow it to sleep normally again (when it is idle for 3 minutes).
To simply explain it, i-Server is for real-time single day use such as for hunting with your dog or visiting a large off-leash park. While SMS mode (on-demand tracking) is for weekly use which offers the longest lasting power on battery.
Below is the list of commands you can use to customize the report time and sleep functionality of your PeTrack unit. You can send any of these commands as a text message to the PeTrack to change the unit's internal configuration. (Interval time is in minutes with 000100, equivalent to 1 minute, as the lowest possible number)
513#0000#1#000500 means that the PeTrack will fall asleep after 5 minutes (000500) of being idle. You can reduce the number to force the unit to sleep faster.
512#0000#1#000500 means that the PeTrack will send reports of its location every after 5 minutes (000500).