It takes less battery power to keep them in the cache for easy access later by the OS. Backing out or hitting home button is fine. The apps that drain battery are the ones that sync, refresh themselves, or access the internet. I have sync off and refresh things manually. You can go to settings, about phone, battery, then battery use to see what is eating your battery. Some apps like mail eat up battery if it is checking for new mail like every 15 mins or so.
You can use a mini manual task killer if you want just don't overkill things and make sure it is never set to auto kill apps. I personally don't use one.
anyway to remove the names of apps on my screen without downloading a special app? i know what all the apps are off the pic alone, dont really need the name too. thanks