I have a Sansa View 8gb and the battery would die like within like 3-5 hours but when I connect it to my computer and go to properties I found that it was charged 84% what should I do about it?

What you need to do is let your player die. Then after it is dead keep turning it off and turning it on till it stops responding. This will run the player out of all battery charge. Then you will keep turning it on so that you can deplete the battery charge that your player sets up as a backup power. Then you need to plug it into your computer and let it charge all night. This will reset the player battery memory so that you can have full charge again. If this does not work your battery might be going out and you should look into either replacing it or investing into another mp3 player.