the real problem is the camera doesn't have an RTC button cell, if it did none of this would be needed, unfortunately it's a battery based design which has been modded (hacked poorly) to use capacitors
As I found, it can be re-hacked
and RTC cell can be added very easy : I used CR2032 laptop backup battery with wires.
Just disconnect D3 that supplies RTC power and connect 3V battery (+) to this point. The (-) of the battery connect to any GND point.
I suggest to make 1st connection via 10 kOhm series resistor and to measure battery discharge current: the scale is 10mV/uA for voltage measured on 10k . In my measuring the RTC consumption is about 1.5uA, that gives for 225mAh CR2032:
(225000uAh/1.5uA/24h/365d) *0.75= ~12year. (0.75 is 25% self-discharge factor).
The battery should be placed as close to the PCB as possible due to speaker, thus I didn't use any glue.
I tested it for ~24h, seems to be OK, before it lost date in ~5-7 hrs.
About a question: why not to do this in a "classic" way with 2 diodes to prevent battery discharge during power-on? The answer is that this causes more bad than good
. I checked this point, it works, and this can really save battery power if you drive more time than the car is in standby. But my car is 80% of time is in standby, so I can save only about 20%. But even for good schottky diodes leakage at hot temperature (during parking) is 2-4 times more than RTC consumption, thus we save 20% but loose 300%. You can use low leakage silicon diodes - but their voltage drop is too high and you also loose battery lifetime. If you need - you can place 2 diodes - it works, but don't use original D3 - it leakage is unacceptable