Vtech phones go dead when I try to use them

We got these phones used from Goodwill (possibly sketchy, I know). There is One main base and three separate mini charging bases - so four cordless phones total. We have let them charge undistubed for two full days. I have used one that works and had a normal conversation on it, but they have decided to not work at all now. (We've only had them a week tops) Sometimes they work, and you can answer calls in and make calls out, but they are consistently dying when you try to pick one up and use it now. As soon as you hit the send button, the screen goes black (as if it were dead) , so we put it in the charging station and it says "charging" and wont go to its normal state for at least an hour, and then it will do the same thing again. Do all of these phones need new batteries? What would cause this? When I tried to register them or whatever I couldnt because they would keep dying and doing the same thing. I know that the phone line shouldnt be an issue because the cord phone we have works fine.