The way customize works is there are 17 icons, each one representing a different percentage. If you start with 1 and keep opening them you will notice the percentage increasing.
Listen. When you downloaded the theme all the png's are labeled as Battery_1-17. You need to take out the "_" and replace it with a "-" FOR THE FIRST 16 PNG'S. Then rename the Battery_17 to just Battery. Then upload all 17 images into Customize and it will work. next time do a search or read the guides to the left. This has been discussed several times.