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 ...
8 "Free" and "on the house" both mean that you don't have to pay, but the inferred meaning is slightly different. If something is "free" it is without charge. For example, you might receive a voucher through the mail that says you are entitled to a free drink if you hand the voucher in at a bar.
I want to make a official call and ask the other person whether he is free or not at that particular time. I think asking, “Are you free now?” does't sound formal. So, are there any alternatives to...
Yahoo News Australia: Experts Reveal the Best Way to Remove Ink Stains From Clothes
Yahoo Style UK: How to Get Ink Stains Out of Clothes: 3 Easy Methods That Work
How to Get Ink Stains Out of Clothes: 3 Easy Methods That Work
Tough laundry stains like those from soda, ink, and wine may seem insurmountable, but there's a naturally derived cleaning product that can remove them easily.
AOL: The Best Ways to Get Ink Stains Out of Clothes, According to Experts
The Best Ways to Get Ink Stains Out of Clothes, According to Experts
Yahoo News Australia: The Best Ways to Get Ink Stains Out of Clothes
Add Yahoo as a preferred source to see more of our stories on Google. Keep reading to find step-by-step instructions for using rubbing alcohol, ammonia, or nail polish remover to remove ink stains ...