I have implemented a new plugin for showing battery icon and remained power percentage on lxqt-panel.
Code is put here: https://github.com/waynecw/lxqt-panel/tree/master/plugin-power
This plugin periodically checks /sys directory to grab the latest battery information, and shows a corresponding icon and percentage on the right side of lxqt-panel. The current support icon themes are "gnome", "oxygen", and "ubuntu-mono-dark/light".
Please feel free to play it, any comment is very welcome.
I hope this plugin can be integrated into lxqt-panel, and if no problem, I will pull request to the main repository.