How can I fix my seimens fujitsu lifebook c1020?

I had a problem with running on the battery,I replaced it,but it still does not work.The battery if full and is being charged.It works 100% on the power supply.
I have taken it to the local agent and they quoted for a new mother board.I am an electronics technician
and I know this is a easy way out.I would like to know how the power connection connects to the battery when there is no plug inserted.I have pressed F6 and have configured the battery
Help Angelo