On the iPhone 4S and 5/5C, Argus uses 25-35% of the battery daily, mainly on tracking steps.
On the iPhone 5S with Motion Activity Service (M7) co-processor enabled, Argus does not use additional battery for tracking steps.
If you start a GPS-enabled activity log, your battery consumption will increase considerably. GPS-enabled activities include cycling, hiking, commuting and other activities that require you to track your location. Logging these activities allow you to see a map and statistics including speed, elevation gain, average pace of the distance you covered.
Please keep in mind that battery capacity and life decreases over time. Older devices such as the iPhone 4 or 4S will lose battery much faster than newer devices.