I want help with selection

[MartinTriesGimp]

   
I want to make transparent pngs of 128*256 of each of the battery load symbols. How to select and export in gimp.

[Espermaschine]

Not a good idea to upscale these images.

The symbols can be easily rebuild with the rectangular selection tool.
If you put each charge bar on its own layer, you can turn them on and off as you need it for exporting purposes.
The rounded batteryshape can be made by using the rounded corners option, turned into a path and stroked for best quality.

[MartinTriesGimp]

I'd like to use these tho.

[rich2005]

There is a useful filter for extracting 'objects' in the gmic_gimp plugin. http://www.gmic.eu A bit overkill for just that function but a great plugin.

Not sure if you want total transparency or...what so refer to screenshots 

https://i.imgur.com/jS4XmzH.jpg
1. Add transparency  to the image Layer -> Transparency -> add alpha channel. 
Color -> Color to Alpha to remove white.
2. Using the Gmic plugin extract objects. Default values work with this one.

https://i.imgur.com/1NM83PT.jpg
3. That separates into individual small layers but in the same layout as original. Which might be enough for you.
4. Use the Align tool. Shift-Click on each 'object' to select all.
5. Align to left edge
6. Align to top edge

https://i.imgur.com/zNVZEL5.jpg
7. Use Image -> Crop-to-content to trim the image.
If you need to scale, Image -> Scale The original had no antialiasing so set interpolation to None.
8. For that single bar, manual fix. Copy from top layer, paste in bottom layer.

I am sure that will baffle you initially but please practice. Small gimp xcf image with layers attached.

[Blighty]

I re-made the batteries in Inkscape. From there exported .png files. The zip contains the Inkscape file and a set of battery symbols. Had to change the aspect ratio slightly to fit 256x128.

To resize the image: do that in Inkscape and export for best results.

To change colour: Switch on the layers alpha lock and bucket fill with a new colour.

[Krikor]

I got this gif by following the steps taken by rich2005 in post #4.
   
But I agree that both Esper and Blighty have made suggestions that the quality of the result will be much better.
Changing to 256x128 compromises contour aliasing.

[Espermaschine]

Lets keep the crusty edges tho.