I created a tool that can batch reisze images of different types (png, jpg, gif, svg, psd, 9-patch..). Uses hiqh quality scaling algorithms and supports certain lossless compression tools like pngcrush. There is a GUI and command line ui.
https://github.com/patrickfav/density-converter
In your case you would set the source scale factor to 2 and check "skip upscaling" also set the platform to Android.
