Chargers were given out as gifts for early purchance a while ago. Recently they can be bought straight from EA as a gift using a token. 10 bucks.
They are ethereal mounts, with unique graphics, and of course cannot be killed since they exist in your backpack as statues if you dismount them.
Anyone can ride them, thus highly sought after by younger players who don't want to wait 3 years to get a regular ethereal mount.