A new kind of gadget is now making such criminal methods unnecessary. It is the Noke electronic padlock (pronounced "No key"). It is made of specially hardened, rust-free stainless steel and tolerates temperatures of -23 to +65 degrees. It comes with Bluetooth 4.0 and can be unlocked using a free smart phone app. For it to work, you only have to press the lock's U-bolt. The lock then connects to the app and it opens. The smart phone can simply stay in your bag.
Also, finding duplicate keys for friends and relatives or club colleagues is no longer necessary. Using the app, you can set access authorizations and times and cancel them again at any time. Every time the lock is open or closed, it records the action.
If the lock runs out of charge at any time, no problem, it has a conventional CR2032 button cell that is easy to replace.
If, on the other hand, your smart phone loses its charge, all is not lost. Using a self-configured pressure rhythm, you can press on the U-bolt and manually unlock it. If you forget this rhythm, then all you can do is recharge your phone as quickly as possible, which is still less expensive than using the bolt cutters.
You can order the smart lock online here (directly from the developer) or e.g. from this site, the price ranges from between € 60-70.