Yep. Garmin GPS units use a grounded X pin on a mini USB cable to determine if it's connected to a PC or plugged into a Garmin charger. Technically, this is out of USB spec and they shouldn't even be labeling the plug as USB on the unit. If you can find a mini USB cable where all 5 pins are connected to a wire, you can simply ground pin X and most Garmin units will charge off a standard USB charger. Others, that are more picky, require a resistor. Unfortunately, because standard mini USB cables never use the X pin, cable manufacturer's never connect this pin to a wire. Thus, it's nearly impossible to find a USB cable that you can hack or make work properly with a Garmin.
On some models, you can connect a standard USB charger, wait for it to go into HDD mode, hold the power to turn it off. While still plugged in, hold the power to turn it back on. This forces it into navigation mode and allows a standard USB charger to work.
I've also gone away from the Garmin in favor of a smart phone with GPS. My RAM universal mount ensures than pretty much any smart phone I have in the future will be compatible.