How can I see what kind of car charger I have? I noticed that when using navigation plus GPS my phone (Galaxy S2) still discharges a bit even so its connected to a car charger.

While googeling, I found out that regular USB chargers only charge with .1 amp but since a car battery isn't drained so easily, there are also car chargers that charge with .5 amp.

Is there a way see on the phone how much its beinbg charged with ? My phone only displays "USB" or "AC".

I'd like to find out if buying a "fast charger" would make any difference or if I already have a charger that supplies .5 amp.
Look on the charger for where it says "output".  It'll say 5V, 0.5A or similar.