You can probably safely get at least 2-3 15 minute flights from your battery as long as it is fully charged and in good shape at the beginning of the day. If you haven't already done so, it's really a good idea to invest in a cycler/charger and a volt meter or battery tester that applies a small load. Using a good charger will make sure they are up to peak capacity and a cycler will prolong their life and let you know the condition. Put the meter in your field box and check your receiver pack between flights. It is cheap insurance that avoids a costly failure. I've seen several people take off with a questionable battery or try to squeeze in the "one last flight". It usually turns out ugly.