I had been using only Ubuntu in my laptop for nearly two years, and the battery life with Ubuntu 16.04 was pretty long. It would last for nearly 10-12 hours. But after upgrading to Ubuntu 18.04, it only lasts for about 3-4 hours (normal light use) and the percentage of the battery decreases with every passing minute. Is there any fix for it?
First read this Ubuntu Help article about Power & battery
If not enought you may want to install TLP
TLP brings you the benefits of advanced power management for Linux without the need to understand every technical detail. TLP comes with a default configuration already optimized for battery life, so you may just install and forget it. Nevertheless TLP is highly customizable to fulfil your specific requirements.
Install TLP :
sudo apt install tlp tlp-rdw sudo tlp start
Then customize suspend setting : System Settings -> Power -> Suspend & Power Button.
I had same problem, and I finally found a solution, (but it may not be your case).
When you log in there is an option button, where you can choose from Gnome classics, Ubuntu and Ubuntu on wayland. I have been using Ubuntu on Wayland (because of some functions), and with this option the battery lasted max. 3 hours. So I changed it to Ubuntu, and now it works perfectly. I also updated the Kernel.
Hope it will work for you.