No battery back up in the base but the instructions that came with the set indicated the phone base station will work in the event of a power outage so I would guess it will still ring but unlikely you could use caller id and announcing the caller in a power outage. This is the only corded phone the base station is a corded phone so that one will work if you suffer a power outage at least you can still make calls like people did before all these fancy extras like caller id call forwarding and such came along!

I am not sure what you mean by transfer from one handset to another. If you mean incoming calls all the handsets ring when a call comes in so you can pick it up wherever you are. If you mean when you have already answered the phone and want to take it in another room or another handset you can just pick up the handset where you want to take the call without hanging up the one you answered it on and once you pick it up on another handset you can hang up the original set you answered it on. Or if you mean you take a call and would like someone else to listen in and be part of the call they can just pick up any handset and the call will be there. Sorry if this is not what you had in mind with your question! There is an intercom function as well on the handsets so if you want it for business purposes there is probably a more sophisticated way of transferring rather than walking to another hand set but I am sorry I don't know how that works.

I cant tell you about CHarter specifically but I have cable and also the voice mail that comes with it and it is able to be turned off completely since you really don't need to be checking your voice mail and the answering machine but if you are too busy to get to it it works fine with both as well. It will show you if you have answering machine messages the red light flashes and press the flashing red button it will allow you to listen to old and/or new messages. For my system with Comcast I need to dial my number to get Comcast voice mail and they give prompts on what to press next to listen to your voice messages and after you may save them or delete them. You will also see who called and didn't leave a message on your missed calls id and then leave them on or delete them. As for the other handsets that is correct they just have the power cord to plug the charging base into an electrical outlet but no phone jack. This is great for enabling you to put an extension phone wherever you want even if there isn't a phone jack in the room i.e. a porch or probably would work in the basement though I haven't tested that. Or put it in a laundry room wherever you want you can put it or just carry the cordless with you if you don't want to leave it in the room permanently.