Very true.
Fully charged = fully charged.
If you have tested after charging and its at 8.41v then something is wrong.
The battery sounds defunct and its not holding the charge anymore.
Easiest way I can think of to diagnose this, is to run with another battery from someone who can assure you its working ok.
If you still get the blue light and cut off power then something else wrong, but I would guess that (if you meter readings are right
) its the battery thats the problem.