This is how it works:
It is possible to top up your M-Bäderkarte with a minimum amount of € 25 at the tills.
Higher amounts than this can be freely topped up in € 5 steps. Irrespective of the top-up amount, a price advantage of 10% will be stored on your M-Bäderkarte. When you pass through the turnstile with your M-Bäderkarte, the discount is applied to the rate valid at the time of admission and deducted directly.