For batch processing, I suggest giving Photo Resize Magic a try, which is lightweight and a small 0.5MB download.
Even though it was last updated 8 years ago, I never had any issue with it even with Windows 8.1. It does basically what I need for resizing, i.e. resizing to 50% or 25% the original size or resizing to within a custom dimension.
Once installed, it shows "Photo Resize Magic" as a right-click option on folders.