Hold the battery cable close to the connector and carefully "walk it out" by pulling parallel to the motherboard rocking the connector side to side.

Grip the cable as close to the head as possible to avoid damaging the socket.

You can also use a pair of angled tweezers to grip the connector head and pull it straight out of its socket.

If you're having trouble, insert the points of your tweezers into the small rectangular holes on top of the socket and push the connector out.