It is 24 months.

All sales in Switzerland have a minimum warranty of 2 years.

Having recently purchased this battery I can't comment on its life, but it was well worth it as it has a good charge time and my Dyson has extended its life and it works better than ever.
Very happy with this purchase.

I don't know how long it is guaranteed but it is better than the original one as it has charging status leds and holds up very well when used.