If your battery is draining, it's most likely because of an issue with an app crashing or running out of application memory, and an iOS update alone will not resolve the issue. there isn't an inherent issue with devices that a software update will fix - only individualized troubleshooting or doing a full restore of the device will
To correct battery usage problems follow these steps:
1. Backup your iPhone using iTunes or iCloud.
2. Use iTunes to completely restore your iPhone as new.
3. Monitor battery usage to see if it is normal. If not, you may have a hardware problem - if so, contact Apple support.
4. Restore your iPhone from your backup above.
5. Check battery usage to confirm that it is normal.