23-03-12, 03:37 PM
(This post was last modified: 23-03-12, 03:39 PM by Falcon 269.)
Battery is knackered. You could tell that by the 12.5v reading when it came off the charger. Should be 12.8v across the terminals on a good battery fully charged. All the subsequent symptoms confirm it. 
You can test the alternator charging output by putting your voltmeter across the terminals when the motor is running. You should be reading 13.6 - 14.0v at 5k rpm.
You can test the alternator charging output by putting your voltmeter across the terminals when the motor is running. You should be reading 13.6 - 14.0v at 5k rpm.