That's the benefit of the 530, 830 and 1030. They have dedicated power connectors on the rear of the mount which connect up to the Garmin external power pack, so you don't have to use the USB port for charging from the external battery. You can use an external power pack on other units, but you end up having to use the USB port for charging. The Garmin Charge power pack only works with the Garmin flush mount though.
Ah the piggyback packs? They've had enough from me, I'm not giving Garmin any more money, I'd rather use generic battery packs and USB. You can then have multiple packs, choose sizes depending on needs, etc. How do you charge the external Garmin packs? Still USB?
Yep, the battery pack mounts underneath the head unit and has output pins which connect to the charging pins on the back of the head unit. Normal USB micro port on the external battery.
That's the benefit of the 530, 830 and 1030. They have dedicated power connectors on the rear of the mount which connect up to the Garmin external power pack, so you don't have to use the USB port for charging from the external battery. You can use an external power pack on other units, but you end up having to use the USB port for charging. The Garmin Charge power pack only works with the Garmin flush mount though.