My neighbour has a well-worn Transit which struggles to start every few days. He discovered that the alternator was shaking itself to bits with several of the bolts loose or missing altogether ! It's now been tightened up again. The battery's about three years old and short journeys are probably a contributory factor but what voltage should there be across the battery with the engine ticking over ? It's presently about 12.7 volts which doesn't seem enough.
I don't think the belt feels tight enough and he says it has squealed on occasions, probably when the lights are on but there's no adjustment left on the bracket. Can a belt stretch beyond it's adjustment potential. Seems like a poor design feature. It's not particularly cracked up.
Andy C