I think you will always struggle against 'fair wear and tear' when making a warranty claim.Thanks for that.
Reading;
A 2 year warranty is offered with all Shimano products from Chain Reaction Cycles (3 years on Dura-Ace and XTR products).
Would this be guaranteed or wear and tear, as I think this is going to be happening about every six months from my experience.
The worn one is original Haibike unit.
But the longer warranty may indicate Shimano expects those products to last a bit longer.