Yes this is indeed a very good question. as afterthefact have mentioned, Fido does not sell stand-alone replacement batteries for the ZTE Wireless Home Phone. Which mean If you are still under your 1year warranty then it's best to contact Fido customer support so to have the device exchange/replace with a new one at no extra cost. Any Fido store will be unable to exchange the device, even at the point of purchase unless if you're still within the satisfaction guarantee which is 15days maximum since the device was purchased.
Hope this helps.
Hello ShadowPatches, Good Question!
As far as I know Fido does not sell stand-alone replacement batteries for the ZTE Wireless Home Phone.
If you are still covered under the 1 year manufacturer's warranty you can try visiting a Fido Store that participates in the Repair & Loaner program. Otherwise, you can trying asking the manufacturer at firstname.lastname@example.org The model we sell is the ZTE Wireless Home Phone WF 720.
That being said, I'm surprised you would need a replacement since the battery only gets used during power outages....
Best of luck!