My 3 original batteries in the combobox each have 2400 mAh! Of course, the flight time depends very much on the wind conditions. In calm conditions, up to 30 minutes is quite realistic! In stronger winds, the drone has to fight harder to hold its position, so it will stop a little earlier. The battery also runs down a little faster with the prop guards.
But I've never had any major problems, especially as I have three batteries to change.