Hacking Gaming Hardware Misc GBA GBA Lithium Battery is draining out when OFF.

MetoMeto

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First of all, hello!


I recently installed this screen into my GBA. The GBA is 40 pin motherboard.
According to a tutorial on Funnyplaying i needed to remove "C54 capacitor" if its 40 pin motherboard (which it is) from it. (i don't know why, what this accomplishes, and its optional, but i followed tutorial even though it didn't said why to remove it)

And i also did this battery mod, except i didn't used the battery in tutorial, i used two switch joycon batteries (3.7V / 525mAh each) connected them in parallel to get 3.7V / 1050mAh
So now i have backlit screen and lithium batteries inside my AGB.


Here's the problem and reason i'm writing on forum:
I can charge the battery using 5V/1A usb-c sharger from my phone, it charges fully in about 1.5h's.
It plays pretty well also, everything is great, except when i turn off the GBA and leave it for about lets say two days, and try to use it, its eather almost empty (red light) or empty completly.
Cant remember but basically its 2,3,4 days being OFF and its empty.

On other hand, my GBA SP, can have charge for months with it being OFF, and when i decide to play it after a month it still has plenty of juice, like i charged it jesterday.
I cant figure whats the problem, but i did poked with multimeter on batteries ends to check DC voltage, and it is disctarging slowly at rate of... well lets say like this
i checked the battery at 01:30 and it was showing 4.084V, than when i woke up at 09:00 and checked it it was 4.078V and now its 16:15 and its 4.075V.

I dont understand what can be draining it when its turned off by the GBA switch. I also have 3 of these charging boards, i tried another and same thing.


Any advice, help, guide how to test and what could be the cause?
 

FAST6191

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Ah hunting down quiescent currents.

Does your multimeter have current mode? You can tell some things from voltage profiles about the discharge current but it is far easier if you can measure current, even a basic one should have something in this if it is draining that fast.

Parallel batteries can be the cause. If one is at a higher level/less health or charges faster than another then the voltage can go from one to the other (possibly after one reaches "full" charge faster and signals a stop and drop things that way. I don't know if the joycon batteries will have much to prevent this from happening.
Might be worth taking one out of the circuit and while it will obviously then halve or worse the capacity it will help with this.

I don't know where any extra wires will come into the mods you have done -- the switch might turn things off but if some guide screwed up and put the say new screen before the switch comes into play (or otherwise bypasses the switch) then you have your answer.

Any wires or things that are shorting inside that you can see? Sharp solder joins and pinched wires can poke though soft plastic wires more than you think. I have not seen any particular failures of internal components thus far but I can't rule it out -- both age of device and exotic mods mean we could be in the weird and wonderful failures scenario.

On the capacitor I don't know its function in this scenario. Noise filtering and voltage spike smoothing are the usual guesses. Larger ones might actually provide some power but unlikely in this. Removal tends to be to change regulation (some use capacitors for this rather than resistors), block discharge of some form or change timings (RC timer circuit having C(apacitance) as a notable component), decouple something on a chip if it is pulled to ground or something (usually to set a setting on the chip) but I would have to have a look to see.
 

G25900

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To add, it could be the charging board itself, I know there's been history of certain board designs having issues with drain (And there's also history of others copying someone else's flawed design then not correcting it when the original is fixed), some can be fixed by removing something on it, others need a whole new board.
 

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