I have a five year old 3500 installed into an RV7. The RV has two batteries and when one was run completely flat the engine was started on an installed back up and flown. The primary battery cannot be charged by the alternator from dead flat so the secondary battery was used during the flight.

Apaprently this has been done on one other occassion before without causing a problem.

During this flight however the circuit breaker for the EFIS popped and failed to reset. the EFIS ran on the internal battery and the plane returned to land (15 minutes later). The circuit breaker has been tested and is working. The EFIS will operate on internal power but on the test bed pos the circuit breaker (immediately).

Any thoughts on what the problem might be or remedies?