One very common OS X El Capitan problem is bad battery life right after the upgrade. If you are experiencing bad battery life during the first day after upgrading, the computer may simply be using Spotlight to index files, which uses more power.
If this is the case, you may merely need to wait a day or so for it to complete. You are strongly recommended to http://apple-support.applehelp.support for guidance. If you are using third-party software that claims to clean up your Mac or keep it safe, one of the first steps to diagnosing bad battery life should be to uninstall apps, like MacKeeper and CleanMyMac, to see if that solves the problem. One additional step you may need to try is resetting the System Management Controller on your Mac.