try pushing the pins that contact the battery so that they bend down just a little bit. I myself have had this issue with a geo+ i used to have. A couple other threads have been on the same issue. Usually after someone posts this bit of info the thread dies, so i guess it worked for them too.
You cannot use an Ego board in a Geo. Ego and Geo solenoids are driven differently and you will experience problems.
The problem that you have is probably due to paint on the underside of the circuit board (underneath where the microswitch is located) causing a short circuit in the battery monitoring circuitry. Use alcohol and cotton buds to clean the board. If that doesn't help then contact a Service Centre.
Steve 'Flash' Monks