Mint Cleaner battery charging issue:
After several weeks of testing, I realised that this is a battery charging issue and is not due to the cradle charger as shown in the video. I had left Mint Cleaner turned off for too long and the battery has discharged itself too much. When you tries to charge it back, it will sound out the alarm after several mins of charging.
To reset this battery charging issue, you simply have to press and hold on the "On/Off" button and then press both the "Sweep" and "Mop" button at the same time.
Mint Cleaner will stop the alarm and continue to charge as per normal. If the alarm continues to sound again after several minutes, perform the same battery reset procedure again. I have to perform this battery reset procedure for 4 times before my Mint Cleaner decides to quiet down and now it is happily sitting on the floor with its ever cheery blue light waiting for his master's command.