It is a commodity USB cable that is frequently used on cameras, memory readers, and other USB devices. It is interchangeable with such products and it's quite convenient to be able to replace a lost or damaged cable with one from a local office supply or retail store.

Specifically, you need a USB-A to USB Mini-B cable and they're commonly available for under $10USD - with a little shopping you can find them for under $2 and sometimes even in dollar stores.

Yes. The GPS will receiver power from the USB cable when it's available. In this mode, you may even physically remove the batteries.

No. Recharging anything that accepts AA batteries generally requires special circuitry to prevent overcharge (and thus leak or explosion) and and a physical switch to tell when rechargeable batteries are installed; these GPSes contain neither.

Some of Garmin™'s other product lines do allow charging from USB. Those models include Garmin Nüvi™, Garmin Forerunner 305™, and Garmin Zūmo™.

The USB 2.0 standard defines three speeds: low (1.5Mbit/sec), full (12Mbit/sec), and high (480Mbit/sec). The last of those is sometimes erroneously called "USB2", but that's inaccurate. This GPS uses a full speed interface.

For waypoints, tracks, and routes that's usually not a burden but when transferring maps, removing the MicroSD card and placing it in an external high speed reader can greatly speed the transfer time.

Garmin eTrex Legend Cx™, Garmin eTrex Venture Cx™, and Garmin eTrex Vista Cx™ have only USB interfaces. There is no serial connection.

Garmin 60Cx™, Garmin 60CSx™, Garmin 76Cx™, and GarminG 76CSx™ unit have serial ports provided in the traditional Garmin™ four pin round connector that can also provide power.

If you place any value on your time, I wouldn't particularly recommend it, but pfranc does make the necessary connectors available.