By saying the battery might not be good for an RTH to 500m, or it will take an unnecessarily long time to climb up and descend shows you are missing the point. Just think about it for minute and consider who else might be using the airspace up to 1,500 feet above wherever you fly your drone. Ask yourself the question, Can I legally and safely fly my drone there? If you can tick these boxes then fine, I will take the following back:
Everyone's circumstances will be different, so there are occasions, when RTH higher than 120m can make sense & I understand this. But for the vast majority of us, the primary consideration for establishing an RTH should be Safety. Step one should be: How high can I safely and legally fly the aircraft in this airspace? If you do not know the answer to this, well you should perhaps give it some consideration, instead of worrying about battery life. 120m will usually be close to the answer in most Jurisdictions. Once this is established, any RTH at or below this height that avoids obstacles will prevent a collision, allow your drone to get home while keeping you SAFE from causing an accident and legal to boot . It is actually a pretty simple process to use the Mavic to do a survey and establish the height of obstacles in the area in which you fly too.
Setting RTH 500m is a fairly good indication that you have NFI what you are doing..