Insert the point of a spudger under the middle of the battery connector's long edge.

Lift and disconnect the battery press connector from its socket on the motherboard.

This will require some force. Don't pry against any resistors or chips.

To re-attach press connectors like this one, carefully align and press down on one side until it clicks into place, then repeat on the other side. Don't press down in the middle. If the connector is misaligned, the pins can bend and cause permanent damage.