Is Qi / wireless charging safe? Heightened temperature not an issue? (Nexus 7)

A friend of mine told me, like it was a fact, that qi (wireless) charging is not safe and it damages battery because it heats it. I just bought one charger, but would like to avoid damaging my Nexus. Could not find out any information about it on the internet though, which makes me even more sceptical, that it just might be a rumour of some kind. I am currently charging right now and it is getting kind of warm. The temperature according to a system monitor is just 32 degree Celsius. Seems normal to me.