my iphone SE takes 5 hours to charge 100% and drops to 42% in an hour and a half. got this phone new in may. any ideas as to why?

This may be because you have too many apps open simultaneously. I am not a tech person, but I am pretty intuitive. To see if your apps aren't closed out after using them, double click on the main control button (not the power button, but the one that is in the lower center of your iPhone. So, double click on it and you will see all of the apps that you have used that weren't closed. They don't automatically close after you use them and suck energy out of your iPhone. In an upwards motion while placing your finger on the screen, whisk away the app and do that til there are no longer any apps on your screen. This will help reduce the energy leaks due to open apps, but there are many other reasons, but this is the easiest and most effective one to start with. Y

Make an appointment at the Apple Genius Bar for service. If you need to find an Apple Store - Find a Store - Apple.

Try checking Settings > Battery and see what apps are using the most energy, report back here if you can.