The following explains what to do it the batteries have leaked in a Genius Room Thermostat.
Batteries can leak if they are left fully depleted whilst in a device, irrespective of the battery type.
The app provides a warning when the device starts to report a low battery and on the Room Sensor this warning can be displayed for over a month, to help prevent this from happening. We recommend getting replacement batteries when the low battery warning is first displayed to avoid batteries leaking and damaging the device. As the batteries leak only then the device is not properly maintained, devices which are damaged due to leaking batteries are not covered by the warranty as no manufacturing fault has occurred with the device.
In the unlikely event that this does happen, we recommend that you get a contact cleaning solution and some emery cloth to clean the terminals.