[tuney]

Many thanks for the replies.

The battery is relatively new and was tested at autozone not long ago and was then fine.
I have taken the cables of the battery and cleaned the terminals, no visible signs of corrosion.
I will try replacing the cables in case of interior corrosion. This may be a problem as the flashing dash lights and door lock problem started after I changed the old battery. The 'alternator' problem has only recently started and may well be a seperate issue.
I am taking the car to autozone today for them to test the alternator and battery.
The car has always started fine, as if there is no problem but the battery guage is reading low and near zero when lights, window heater and heater are on.

The serpentine belt has not been changed in the last 60k miles.
Could the whinning noise be a slipping or worn serperntine belt and the low charge from alternator be caused by the belt slipping and rotating the alternator enough ??

Visibly the belt looks ok and is within the wear indicators on the tensioner.