And you won't believe how much it cost!
I fitted a new alternator, a new starter/solenoid, replaced the associated wiring, popped in a new handbrake cable and switch, and topped up the diffs. Now I have a car that starts on first crank, charges it's own battery, is able to hold it's own weight on a hill, and has a real working handbrake light. £204 total spend.
Sorry for the clickbait.