I believe Charter give residential customer a dynamic IP. But it has a very long lease time, probably several days.
So if your modem is not down for several days, you basically will get a static IP.
My experience is it seems that Charter will rotate customer's IP range from time to time, probably every half year.
I'm in California, but right now if I check my IP through IPchicken.com, my name is like xxx.xxx.xxx.xxx.dhcp.unas.mo.charter.com, that's weird, which should be in Missouri, but if I do tracert test, I'm still in California. But my IP might rotate back to xxx.xxx.xxx.xxx.dhcp.unas.ca.charter.com someday.
Every time when they are rotating the IP ranges, I'll have trouble getting online. It usually happens in weekend though.