said by Bob4: said by cablewizzard: said by Bob4:
If you don't have phone service, the battery is used to power the Internet connection.
That's pure, unqualified speculation.
No, it's not. It's from Arris documentation.
So you wanna quote from an uncited source, instead of actually trying it out? Go ahead, cause I've done that (TM802, 2 OV lines, battery): you're losing this argument.
Even if you can quote the source, power-save options in DOCSIS modems (2.0 and 3.0) are generally configurable to quite an extent: ethernet up/down, LEDs on/off, USB on/off, channel bonding (DS and US separately) on/off, disabling of 1 or more tuners - you get the idea, and YMMV by vendor a bit.
Unplugging your TM8XX from AC power with the battery installed and observing the results will teach you that device documentation, especially publicly available documentation, often has nothing to do with how an MSO actually operates its devices.