Pedalo,
To put my experience into this, my powabyke is 8 years old and in the time owned I have replaced:
3 throttles,
3 sets of batteries (about to buy my 4th),
I have serviced the motor (regrease and clean) ,
replaced one controller,
soldered the loom to the controller board due to arcing,
replaced the forks (sheared inside head tube)
new seat post (snapped),
replaced the brakes front and back (poor quality / spring casting failed)
plus tyres, chain, cassette and brake pads as you would expect.
To put this in perspective the first couple of years the bike had an easy life and the battery was neglected (my fault). For the last 5 years it has been used dailyish to commute to work (20 miles round trip) 1500 miles , then 2000 miles , 2400 miles , 2900 last year and currently I have covered 2200 so far.
I have learnt a lot and have had good support (mainly) from powabyke and later this site. I feel the above is fair expectation of the original quality of the bike components used, i am leaning towards a "ping battery" next which will probably see the bike to retirement! (hopefully in a couple of years at least).
Not sure if that helps !
Daryl