My battery will only last for a half of a day on a full charge
As long as the phone is the correct model and build, then yes you can use a refurbished phone. Note that all legacy phones, E1, E2, G1, G3, X1, X2, must be the Republic Wireless model with the custom ROM chip inside. The old Defy phone can not be activated any more.
For BYOP models, enter the model number in the phone checker. Bring your own phone to Republic! | Republic Wireless