Battery Backup supports only phone service provided by your service provider on the modem. Backup Hours vary by Modem model number. Internet Service is not supported on Battery Back-Up. During electrical outage make sure an analog phone is plugged into the Phone Port of your modem. Dect phones are not supported by modems in case of electrical outages Supports various Models including; TM502G, TM504G, TM602G, TM604G, TM608G, WTM652G, TM722G, TM802G, TM804G, TM822G, TG852G, TG862G, TM1602G, TM3202G, TG1662G, TG1672G, TG1682G, TG2472G. PLEASE CHECK YOUR MODEM PRODUCT MANUAL FOR SUPPORTED BATTERY TYPE.