In the grand scheme of things, I am very pleased with the R5 C. The still imagery is fantastic. It runs all day in photo mode on one battery. If I really push it, and things run long I just pop in a spare.
4k video. For that I'd carry two batteries and maybe a USB-C PD. The one I have fits in my pocket and is more than adequate. If you are going to shoot in 8k, that requires a little more planning. In that case a Small Rig v-mount battery set up. Now it basically runs all day unless you are sitting with the oversampling on idle. Press the media playback button and problem solved.
I waited (to upgrade) through it all. R because it was the first mirrorless. RP because it was too small. R6 because 24MP and the R5 because of the over heating which to some extent has been largely eradicated with firmware. The R5 C is still by far superior to the R5
if you are interested in video. Primarily due to its additional codecs. If you aren't, then there is no need.
For someone who primarily shoots stills, the R5 with ibis is a top performer. I wanted more, and didn't care about ibis so much. I paid more and got it in the R5 C. I'm not defending it just because I have one. Its a great camera. Are their things I wish it did differently, sure, but thats been true of every camera I've owned, except my AE-1.
I believe as
@Scenes does. The mkII variants of both cameras will use the same battery size, but like the LP-EN6
H and the newer battery made by small rig, Canon will figure out how to further reduce power draw of the camera and beef up power delivery to some extent. The R5 C mkII being a year or more away doesn't bother me. I have a great camera now. I'll probably be ready for the C mkII when it comes. I've got the glass which should last until I can't hold a camera up any longer. Then I'll be EoL insted of my camera