Good News ! All seems to be working. And the winner of the correct answer in this thread is ....... I tried 7 batteries. 5 of which were brand new. I used one of the brand new batteries for my car key fob.... dead. Tried another... dead. Smelling a rather large rat I have bought some more batteries. Car key fob works. Took known working battery from car key fob and inserted into motherboard.... boots up after plug left out and everything seems to be fine. Other new batteried work in car key fob. A whole batch of dead new batteries (expires 2023). Thanks to everyone who took the time and trouble and replied here. Its much appreciated.