Update from 5.0 failed. Help? (S5 Active, AT&T)

Currently failing at updating my S5 Active from 5.0 on AT&T. The update it attempts to install is 640.54 MB according to the download screen. It then restarts the device, boots and begins the install, and fails at 0%.

Phone has a nearly empty 32gb SD card installed plus the standard 16gb of storage (about half full).

So far I have,

1. Attempted the update using Samsung Kies... Which says my software is up to date and thus doesn't find/attempt any install.

2. Attempted update numerous times on my phone. Failed with free on device storage of ~1 GB, 3 GB, 6 GB. I'm now trying it with 7 GB free (plus 31 GB on the SD card) but I have little hope left.

Phone is plugged in, charging, at 100% for all install attempts. Any ideas?