If you really really must use Lubuntu instead of changing your default session to XFCE (Xubuntu) this is the link you should visit to find some workarounds for your problem which affects many many users apart from yourself. Though you may think at a first glance that the post deals with some bug specific to Lubuntu 13.10, read ahead on that page to find out that the same bug applies to Lubuntu 14.04 too.
It is the reason I urged you to use the xfce session instead of the lxde session which may be good for desktop computers but it is not that good for laptops.
To be able to use xfce4-power-manager full features in Lubuntu, you need to, and I quote from that page:
- You can go to ---> Menu > Preferences > default application for LXsession > Power Manager > Other > xfce4-power-manager > Apply >
Reboot.
HOWEVER, please note that this is not enough and this feature should
be loaded by default, just like it used to be.
- Another solution is to open Preferences --> Default applications for LXSession, then go to the autostart tab and here change the option
"Disable autostarted applications" from the default "config-only" to
"no". You may need to change the settings for laptop-mode from "no"to
"yes". (settings tab).
Note that you need to disable "network" from Prefereces-->Desktop
Session Settings or you will have two nm-applet running at the same
time.
There are other unofficial workarounds designed for xfce power manager to work in Lubuntu, and you can check the answers too just to find another good link to this page where you can find yet another 'working solution' for your problem:
- I had this problem, i unchecked "Power Manager" from "Application Autostart" list in Settings -> Session and Startup and added another
application with this command xfce4-power-manager --no-daemon then i
have not have this problem yet.