Hi,
I need to supply the C3U with 4xAA battery. Is it possbile? Is the maximum input voltage some where specified?
Usually the starting voltage of a AA battery is little bit more than 1.5V. So the whole voltage could be more than 6V. Now the switching power supply of C3U use a HM8089 switching device that has an absolute maximum rating voltage of 6V. There is in series a B5819 diode that could reduce little bit the maximum voltage. but is it enough?

Regards
Gian Carlo