Focus 1.8 TDCi Ghia 2002 clutch and battery?

Hi there.
I live in Spain and have a 2002 Focus Estate (Wagon).
The latest problem started in September 06. The symptoms were:-
If the car started, could not get into any gear. Sometimes the car turned over but refused to start, there as a repetitive knocking noise and "chugging" as my wife put it.
It went into the shop and they diagnosed a faulty clutch. They replaced it and also the flywheel as they said both HAD to be replaced at the same time.
Question 1: Is it correct that the clutch AND flywheel must be replaced at the same time?
Then, about a month ago, the same problem occurred albeit the "chugging" non-starting problem was worse than the starting no gear problem. Back to the shop and they said NOT the clutch but the "bit after it" (possibly drive shaft?). Unfortunately, our Spanish was not good enough to understand. As they said roughly same price as before and we’re broke, we didn’ get it fixed straight away.
However, we recently took it to another garage and they inspected it and said definitely clutch and flywheel needed replacing but they would not do it under warranty and to take it back to original garage. Original garage have now fixed it and said that, get this:-
the battery was faulty which meant there was not enough power to start the engine ’properly’ which damaged the clutch and flywheel.
Question 2: Is there any possible way that a dodgy battery could cause damage to a clutch / flywheel set or is this the BS I think it is?
Many thanks in advance for your help / comments / laughter......
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