The Becker transponder in my DG-300 would frequently give the E10 error. When I changed from my old SLA battery to a LiFePo battery the E10s became a lot less common but still occurred occasionally. If I did get one, I often found mid flight that I could turn on the transponder an hour or so into the flight and it would work fine for the rest of the flight. Mid season last year I gave the connector a serious wiggle and shove into the transponder. Haven't had an E10 ever since. However, every time I turn it on my fingers are crossed.

Larry'