I get about 1,200mA charge no matter how large a 5 volt source I use (and I have one 30 Amp power supply I've tried it with), using the standard cable that came with it. I suspect that I might get a little more charge using #16 or even #14 wire, but that's bulky - about as thick as lamp cord. The phone is built to do 2 things - draw a certain maximum amount of current from the charger (which appears to be around 1.2 Amps in my case) and to stop charging whn the battery reaches full charge (which mine does).
I don't worry too much about batteries, though - the way I treat mine, my 11 year old Motorola SNN5722A battery, sitting in my 11 year old phone, is still giving me about as long a time between charges as it did 11 years ago. (The fact that the phone is 2G makes it useless for anything but voice or text, but it wtill works if I need it.)