First, install Solaar to see the battery level on the taskbar

sudo apt-get install solaar

To remap the keys, install

sudo apt-get install xbindkeys xautomation

Then, launch xev to get the keyboard or mouse event to bind

xev

# grep button
xev | grep -i button

Create the configuration file for xbindkeys

nano ~/.xbindkeysrc

Here is an exemple of this file that map the Back and Forward buttons to BackSpace and Return respectively

# Back button => BackSpace
"xte 'keydown BackSpace'"
 b:8

"xte 'keyup BackSpace'"
 b:8 + Release

# Forward button => Enter
"xte 'keydown Return'"
 b:9

"xte 'keyup Return'"
 b:9 + Release

To test your binding

xbindkeys -v

To start xbindkeys

xbindkeys

To find key code

xbindkeys --key

// or

xbindkeys --multikey

If you change the key map, you have to restart xbindkeys by following command

killall xbindkeys && xbindkeys