The next most common thing is that the volume images are too big, so aren't caching. Try, instead of images, putting text in there (Also make sure you move it to the top of the text part of your WPS, after you load images). Change your line to something like
%?bp < BATTERY CHARGING|%?bl < BATTERY 0|BATTERY 1|BATTERY 2|BATTERY 3|BATTERY 4|BATTERY 5 > >
Remove the spaces around the < and > symbols, for some reason they wouldn't display even though they displayed before.