CISCO CABLE MODEM GATEWAY BACKUP BATTERY 8 HOUR FOR DPC3939 DPQ3925 DPQ3212

Worth its weight in gold. Fits, works, and less expense than purchase from modem supplier. I am using in Xfinity Cable Modem which is Cisco DPC 3941 T with great success. And have needed the battery several time this winter for short power drops with no interruptions in my phone or internet, and having the modem reset upon loss of power. Highly recomend this battery for this modem. I do not know if battery fits any other modem other than the DPC 3941T.

I can't believe that Comcast makes you go out and buy your own backup battery for the modem that you have to pay for monthly, but I got tired of fighting with them. This battery fits correctly and is apparently charged properly. I have not yet had any power outages to check its reliability.

We have one of those ubiquitous Comcast modem/routers that provides a VOIP line along with everything else, and we wanted it to stay on in a power outage. It's plugged into a small UPS but we figured this would be a backup to the backup so to speak.Installing was super easy. Waited for it to charge completely and then forgot, so we did not actually test it right away. Got that test eventually when the power went out on its own. The modem ran on its own battery before drawing from the UPS, which meant that it stayed on for a long time -- as we hoped.Before writing this I unplugged the modem briefly just to double check (the test you should do) and yes the phone stayed on. So, it works as expected. Note, this does *not* backup power for the internet or wifi part of the router, it just powers the phone line. I suspect this is so people can make emergency phone calls and that's why we wanted it. If you do not have VOIP service, or you want your internet backed up, you'll need a UPS.

July 2017 It's a newly installed battery. I won't know how well it works until the first power failure. it arrived on time and fit the modem and is the correct battery for my modemUpdate June 2019: This product is garbage. I had my first power failure yesterday and the modem died within 5 minutes. This battery should have lasted much longer. I guess you get what you pay for. If I could I would ask for a refund

EDIT: Updating review. Someone else got the same battery, and their "number of cycles" and "actual capacity" numbers are exactly the same as mine. It is possible that these numbers are not accurately reported in the user interface of the cable modem. I am updating the review to three stars until more information comes to light.---OLD REVIEW:I received this battery from amazon, and the description says "Sold by TLC USA and Fulfilled by Amazon."This is a used battery with a large number of cycles on it. The battery, when plugged into my Cisco cable modem, reports the following information to the system. Of particular interest is the "Number of Cycles to date" value and the "Actual Capacity" value.Power Status: ACBattery Installed: YesBattery Condition: GoodBattery Status: ChargingBattery Life: GoodTotal Capacity: 3000 mAhActual Capacity: 2700 mAhRemaining Charge: 1134 mAh (41% )Remaining Time: 1.3 hoursNumber of Cycles to date: 4321Battery Model Number: ModelNumber1.0Battery Serial Number: SerialNumber1.0Product description should clearly state "used".

Plugged right into our DPQ3212 and after about 20mins the battery was up and running. Have tested the battery for over one hour with the power unplugged and it kept the our digital phone line connected with no issues. Please note that having the battery backup does not keep the Broadband connection active. We knew this about the DPQ3212 but purchased the battery because one of our Alarm systems is linked with the digital phone line, and that is our primary concern if/when power outage. Have not tested for their 8-hour claim but the battery at least works well enough to fulfill our needs

Installed and fit my Cisco like a glove. It's now going through the 5-6 day initialization cycle (driven by the Modem's software (i.e., Charge battery for day, fully discharge, recharge for a day, enable). I will then need to check with Comcast if they are monitoring the battery remotely! (seeing as I bought the battery here, not from them at their exorbitant price)!It did not come with the spring-like device at the bottom, but that was not needed for my modem. It did have a light-weight plastic tape-like strap at the bottom in that area that will prove handy when I need to pull it out and replace it in a few years. I removed the Modem from the Surge Arrestor (sp) and plugged it directly into the wall (per instructions in the product box). As my home phone itself has a "wall wart" power supply, I moved that mini-PS over to a small UPS (Uninterruptible Power Supply) that I had previously connected to the Modem. As described by others, during a home power outage, only the phone function will rperate on this Modem's battery, not the Internet.Note FWIW: I am using a CISCO Modem, Device Type: XB3, Model: DPC3939, DOCSIS 3.0, VOICE GATEWAY PN: DPC3939-4068213-K9

I recently switched to COX VOIP and they wanted $30 for the backup battery. I saw this one for $22 and opted for it. Dropped it in the modem and the battery light came on so I assume it was OK. A couple of days later, I pulled the AC plug and verified that the phone still worked so as far as I can say this meets expectations and saves you a few bucks.