BEWARE – If you have the sat nav system fitted extra then you must be aware that wrongly disconnecting the battery can seriously damage the system.
Before disconnecting the battery you MUST wait for the red light on the sat nav box to go out. This will take several minutes after opening the boot, bonnet or any door.
When this light is off you can safely disconnect the battery. Remember to disconnect NEGATIVE first and reconnect NEGATIVE last – this minimises any accidental shorting of the positive terminal on the bodywork.
Make yourself a label to remind yourself – or any unsuspecting garage mechanic – and attach it to the battery.
See …… https://mgzt.info/2021/07/17/battery-disconnect-warning-label/
MG ZT info mods and maintenance 