In the past few years I have been busy with prototyping electric car batteries upto 400kW/1000A. We always used "conductive grease" for all the power terminal to eliminate contact problems.
Conductive grease can be DIYed with graphite powder and some thick oil.
The original
phoenix contact power connector should be rated for higher amps than 5A, but the counterfeits we might see on the Ramps clones are probably less.
-Olaf
PS: Just a copy of what I wrote in another connector related thread...