I have recently received and tested the CN4 generic replacements for the AC-4C.
I found that on the cameras tested so far, they work, even with flash. Curiously, the battery level displays one or two bars out of three. I need to check the voltage, but I believe them to be correct.
I got them from Rex at Viva Power/ Yuptek. His email is adapter insert-a-in-a-circle-here viva-power.com.cn he sold me three with shipping paid to Hong Kong for USD19 in total.