lassig,
I picked up a new TH feeder a few weeks back. I have the solar charger as well. I'm not sure about the older models, but on mine when you disconnect the battery and reconnect, it cycles through a systems check. It senses the solar charger is present and indicates whether it is charging or not and will display the message during its cycle. On actual output voltage, you will need to measure with a volt/ohms meter. As someone mentioned, these are trickle chargers. Their job is to keep a charged battery hot. I had one hooked up to a bay boat for 2 yrs. The battery was always hot.

...when in doubt...set the hook...