Hmm, I have the /sys/class/power_supply/8xlifepo4 folder on my machine, which is using a custom kernel on the Banana Pi CM4 SoM.
The CONFIG_CHECK line in the ebuild was guesswork, based on the headers that the module includes. I might have missed some runtime dependency (if such things exist in the Linux kernel).
I could also imagine that there is still some hardware waiting for prerequisite modules to get loaded - /sys/kernel/debug/devices_deferred - but that’s guesswork too.
EDIT: I just saw that you got an answer in LPC kernel module on ls1028a - #2 by josch - so it is a device tree issue.