RTA

The battery will be the interesting part. Ever sat a car battery on a shelf without maintaining it? Unless a battery is charged occasionally, the chemical composition of them breaks down and they are useless. To be realistic, they would need to be regularly cycled in a car/truck or charged with some other source (solar, wind, generator). I suppose they would decay like apples, etc. The only fresh batteries would be those that have been used regularly since the "start" of the apocalypse, and even then they will deteriorate, so it might be that the only way to get a working battery would be to steal one from someone else.

In-game voice is pretty much line of sight; if you can see them, they can hear you. Typing is slow and whilst you're typing, you're at a high risk of getting killed. The "friendly dance" is the Q and E keys back and forth.