They are indeed supposed to be a fixed 3.5 amps. I have checked a number of them with the mutimeter leads plugged into the 10 amp current port. Check in series with one of the leads. 170 is definately too hot. If it is charging at 10 amps then that can explain the temp , if not then an overcharge is another explanation. It's hard to believe it is much over 3.5 amps, but anythings possible.

As far as battery life goes, 10 amps will shorten life maybe to half or less. Yours has more trouble though than just charging at fast rate. If it was going at 10 amps then it should be done in less than 20-30 minutes.