Hi.
My RV-7 has just spent about 3 1/2 weeks on the ground due to some engine problem.
I've fixed that problem and today it was time for a testflight.
After power-up and just before engine start, I turned off the avoinic master switch as usual and expected the 3500 to start running on it's internal battery as usual, but instead it shut down immeadetely. (completely dark screen).
I started the engine anyway and the 3500 came back up (it initialized the usual way) when I turned on the avionic master switch again.
During the flight, the 3500 performed great as usual.
When I was ready to shut down after landing, I as usual turned off the avionic master switch, but once again the 3500 shut down when the switch came off.
During the last flight before this one, (3 1/2 weeks ago) the 3500 has switched to it's internal battery as it schould, and the stand by battery indicator has shown a fully charged battery.
Does anyone have an idea what the problem can be?
Is it somewhere in the menus I can find the voltage and state of the internal battery?
The 3500 was bought in 2006 or 2007 (I think) so maybe the internal battery is at the end of it's life?