A few issues related to the battery that is draining too fast for Samsung Galaxy Mini, a few tests to make in order to fix the problem. The battery of a Samsung Galaxy Mini requires around four hours to get fully charged. If the smartphone will stay in Stand-by (nothing will be operated on it), it should drain like 3-4% / hour or even less.
Leaving open applications while the Samsung Galaxy Mini is on Stand-by will also drain more from the battery since the processor will run at a higher capacity.
Do the following tests in order to fix the issue related to the battery: make sure to uninstall all the applications that are not being used often and are not very useful, leaving around 80 or more megabytes of free space on the internal memory.
Charge the smartphone for around four hours until it will beep that the device is fully charged. The battery draining issue might be related to an installed application, full internal memory or even the temperature of the place where the smartphone is kept. The battery will experience a faster consumption if the Samsung Galaxy Mini will stay in a cold place (cold room, car etc.).
Samsung Galaxy Mini should last around two days in Stand-by mode, and around one day when using applications, watching YouTube videos etc.
If the battery will still experience issues, view the warranty at the mobile phone operator and ask them to either fix the battery or to replace it.