This is an important step, as it lowers the risk of any shorts happening while handling the motherboard.

The connector for the RTC battery is similar to the speaker and fan connectors. Before removing it, lift the silver flap that's also stuck to a wide cable connected to the motherboard.

To unplug the battery, pull on the connector in the direction of the arrows. It is a similar connector to the speaker and fan connectors. In my case, it required a bit more effort to get it out.

Finally lift and unstick the battery from it's holder and put it aside.