I don't think there's any difference in meaning, although "free of charges" is much less common than "free of charge". Regarding your second question about context: given that English normally likes to adopt the shortest phrasing possible, the longer form "free of charge" can be used as a means of drawing attention to the lack of demand for ...
MSN: Spot 3 differences in the zebra running on the grass. Only 3% can find them in 17 seconds!
Spot the difference puzzles are one of the classic puzzle games that are still going strong in the era of reels and snaps. This ultimate brain teaser challenge tests your observation skills. The best ...
Spot 3 differences in the zebra running on the grass. Only 3% can find them in 17 seconds!