Why would you want to close them all and make your battery life worse?
How do you know they are using up your battery life?
If they are suspended and not using any background services then battery impact will be minimal to none. All you are doing is removing them from memory and increasing the battery usage required to relaunch the app - if you are regularly killing apps you use on a regular basis this will be affecting your battery life even more.
The system will remove suspended apps from memory as and when it needs to - it will prioritise more popular apps over less used apps when purging. Trying to do a better job of memory management than the OS is pointless.
3. Stop quitting your apps in multitasking
Most people tell you that closing your apps will save your battery life because it keeps the apps from running in the background. However, this can actually make your battery life worse if you do it on a regular basis.
By closing the app, you take the app out of the phone's RAM, so when you open it again your device has to load it back into memory all over again. All of that loading and unloading puts more stress on your device than just leaving it alone.
The truth is, apps in your multitasking menu are not running in the background at all: iOS freezes them where you last left the app. Unless you have enabled Background App Refresh, most of your apps are not allowed to run in the background.