Similar issue here.
First charge cycle reached 100% and I started using the laptop on battery power when it suddenly died an instant death, without warning, many minutes before the battery was ‘supposed’ to run out. Since then, I’ve not been able to charge it beyond 55%.
Grepping the boot log reveals the following load failure:
Failed to load DMC firmware i915/kbl_dmc_ver1_04.bin. Disabling runtime power management.
which sounds pretty relevant to me.
Did you find a solution to the problem you were facing?