The only reasons you would have a backup battery in your rented EMTA modem are:
A) You subscribe to telephone service from Spectrum over your cable connection, AND
B) You separately purchased and installed the model SMPCM10 backup battery into the modem housing following the instructions in the user's guide.
You can verify the presence or lack of a battery by opening the housing and looking inside, following the instructions in your user's guide.
In the recent past Time Warner has not provided any model of EMTA modem with battery pre-installed, and as far as we Forum contributors know, Spectrum also does not include the battery, install one for the user, or offer them for sale.