Cheltenham's big rivals are Gloucester City AFC from just the other side of the M5. Of course, they were together in non-league for many years and the year that Cheltenham got promoted to the Conference (and then subsequently got into the Football League) they only did so because Gloucester cocked it up on the last day of the season. If they'd won, Gloucester would have gone up and, who knows, may now be where Cheltenham are in the League pyramid. As it is, they now have to ground share with Forest Green Rovers as their ground was recently flooded and is unlikely to ever be used again and they are in big financial trouble.
No they dont. I have spoken to a few palace fans, (Online, and theres one at my work) And they have said that palace dont consider Charlton as their main rivals. Charlton like to think that palace hate them. Palace consider Millwall and us as the two teams they hate more that anyone else. Charlton Palace is a one-way love (or hate)