I had some of the symptoms described here, but mainly on starting as well as central locking problems. Although irrelevant at first I learnt a lesson that might help here ....
I also tested everything and it turned out that I had two cells in the battery that was on their way out.
The only way I could test for this was to check the SG of each cell. One bad-ish cell caused a low (but not abnormal) operating voltage whilst the second cell failure caused discharge of the battery on the internal resistance overnight. The starting problem was intermittent so the failure of the battery did not occur to me until the scond cell failed completely.
All voltages checked out OK - the SG on two cells were very low compared to the other 4.
check the SG on the battery - it might lead you in the right direction - not only the charge and unladen voltage.