And what is the best phone number to reach customer service at Arris? Thanks 

what specific models are you talking about? 

Details are key. 

Personally, I prefer just purchasing a 3rd party power supply so I can connect other devices to it and replace it as needed. 

Hello Ivy,

Could you let us know the model number of the modem ? so we can let you know the compatibility of Arris Battery . 

Also, contact arris.com/consumersupport for further help.