Adding a clock battery to action camera to retain date&time when changing batteries Campark X25

[flat-earther]

I have a cheap action camera with an annoying trait, every time I change batteries the date & time gets reset and I have to set it again.

To solve this problem I want to add a small internal battery inside it which will keep supplying power to the camera for a while while I change batteries so the date & time is retained.

I have opened the camera and I think there is enough room to add something inside to accomplish this:

The camera is powered by a 3.7V nominal single cell lithium ion battery.
So I need to connect another battery in parallel to ground and battery + on the PCB.

What battery, or perhaps capacitor should I use?
I have on hand such capacitor visible in my photos which will fit, 25V 220µF, would that work?

And should I add a resistor in series with the capacitor to limit the inrush current charging the capacitor when plugging in the battery, if so what value resistor?

[harp]

On scrap pc motherboard you can find smaller size and bigger capacity electrolitic caps for 6.3v... I also seen that for retain clock is used special supercapacitor look like ordinary small battery with tht tabs. You may want to concern to separate your battery from mains one, to overcome discarging system battery for filming... maybe to inspect pcb in off state to see where is present voltages for system standby...

[stj]

find the 32.768KHz crystal and see which chip it connects with.
then get a datasheet for that chip

[flat-earther]

Thanks guys for your suggestions,

The component marked EAFC is the 32.768KHz oscillator, I think it's MC-146. one side is ground and the two pins on the other side are at 0.85V at standby,

I didn't find continuity from it to any pin on chips XR819 or AXP233.
On the other side of the board the chips B649SN and the covered one are BGA so can't test pins.

In standby I found few places at 1.8V, maybe adding a cap there would keep the time? IDK... everything is extremely small so I think I will connect a capacitor to some place on the main battery rail,
I found online 6.3V 2200µF10x12mm capacitor, looks like there's enough space to fit it so I want to try that.

board iT_X16_V1.2 2019.06.24

[harp]

On pc motherboard, cpu rail have small 2.5v caps arround 560uF... if you want to connect it to 1.8v places... I would solder thin isolated wires to that 1.8v points, and connect 1.8v lab psu, dissconect battery, wait few minutes, and take it back and see if time is reset.

[flat-earther]

On pc motherboard, cpu rail have small 2.5v caps arround 560uF... if you want to connect it to 1.8v places... I would solder thin isolated wires to that 1.8v points, and connect 1.8v lab psu, dissconect battery, wait few minutes, and take it back and see if time is reset.

Good idea, but first I want to try if adding cap to battery rail works because it looks easier.

[flat-earther]

Oh no all my photos in this thread have been lost.

I added a 6.3V 2200µF10x12mm capacitor.
I connected the capacitor to a ground and battery rail point I found on the camera's PCB, and added a 150ohm resistor I found in series with the capacitor to limit inrush current when plugging in the battery:


First I taped and glued the capacitor to the lens housing but the cap was too high so the case didn't fit:


Then I moved the capacitor and attached it lower, right on the PCB:

But there was one protruding feature on the camera housing that was still interfering with the capacitor:

So I ground the plastic away:

After that it fits:


I tested it and after changing battery the time is retained now.