The size hint provided by the icon, for example 22-22-foo is to load a less detailed graphic when a smaller icon is requested. On a high dpi screen it will request a larger icon that will eventually be rendered on the same physical area as on a low dpi screen making the icon hard to see due to thin lines.

Reproducible: Always

Steps to Reproduce:
1. Have high dpi screen
2. Look at battery icon in tray
3.

Actual Results:  
It is using the regular Fill icons

Expected Results:  
It should be using the 22-22-Fill icons because it's a small icon