I visited Berlin this weekend, and I bought a 4-pack of single AB tickets (they're €2.80 each or €9 for 4) and ended up only using 3. Is it worth hanging on to the other for the next time I go, which might be a couple of years away or will it have expired by then?
Incidentally, I had this wonderful view of a U5 depot from my hotel room - the Abacus Hotel Tierpark is highly recommended!

Incidentally, I had this wonderful view of a U5 depot from my hotel room - the Abacus Hotel Tierpark is highly recommended!
