1.8 is forcing it to charge faster than it should. Which will more than likely give the pack a shorter life and shorter run times.
I used to charge mine at 1A with my MRC 959 charger just to get it done more quickly, but I quickly realized that the packs weren't holding their charge as long as I was accustomed to (see 12V PS info below). So, now I adjust it to .5A and the charge lasts much longer and the packs don't get nearly as hot when they are charging.
Until I got the "real" charger, I used a .8A 12V power supply to charge my receiver packs. I used it for about 2 years. I just had to pay attention to the temp the packs reached and pull them off when they got around 105F.
I fried the PS when I tried charging my transmitter. Usually when your charging something, the voltage the "charger" is putting out is more than twice (almost 3 times) as high as the voltage of what your charging. This ensures that the current is going to go into the battery as opposed to the battery trying to send it into the "charger". I'm pretty sure that's why I fried the PS I had. 8 NiMH AA's fully charged is ~9.6V (really around 11V) and I think it was pushing back against the PS so to speak and it cooked it.
I'm guessing your 7.2V wall charger is probably less than .5A, so it would be ok to use, but beings it's a wall charger, it probably isn't a good automatic peak detecting charger. You will have to unplug it when the packs warm up, so you will have to monitor them frequently until you get a feel for how long it takes to top them off.
