A rapidly draining battery can be the fault of several things. Typically, a rogue app is the culprit. Anyway, the first thing you should check when dealing with rapid battery drain is to see whether or not "Usage" and "Standby" times are identical. If they are, reboot your iPhone, use it for a minute and then let the device sleep for a minute. AFterwards, check the battery settings to see if the usage and standby times differ. If they are, more than likely you be solved the battery problem. If they remain identical, figure out which app is causing the problem.