Joy-con draining main battery?

[Bigdrago]

Hi!
I noticed that on two of my switch oled the main battery is draining even if they are turned completely off. But this dont occur on my newest switch.

I charged all three to 100% and removed joy-cons. After 5 days I turned them on and all were 100%. I inserted joy-cons and noticed 4 of them started charging.

I thought joy-cons didnt charge from main battery when it was powered off.

Anyone else noticed this? All three have picofly and atmosphere 22.5. Guess I have to replace joy-cons batteries to solve this

 

[thesjaakspoiler]

According to Nintendo joycons don't charge if you completely power down the Switch.

Note that lithium batteries naturally slightly drain themselves.
This can get worse with older batteries.
And there is a very small part of the Switch listening whether the power button is pressed.

Most devices with a battery briefly also start charging once they get power.
When they see that they are already fully charged, then they stop again.

If you;re not loosing a few percent overnight, then it isn't much to worry about.

 

[Bigdrago]

Yeah, I've seen that and that cant be the case here. Battery draining is only when joy-cons are connected.

 

[master801]

iirc the power rail for the joy cons is also used for a different portion of the Switch (I think the fan?), so that may be part of your problem.

 

[lightwo]

iirc the power rail for the joy cons is also used for a different portion of the Switch (I think the fan?), so that may be part of your problem.

I don't know if that holds true; but it looks like JoyCon batteries are connected in parallel to the main battery (source):

My best guess is that the Joycon batteries are simply wired in parallel with the main battery so they charge up to, but never exceed, the voltage of the main system battery because the system does not boost the voltage to charge them which is why Nintendo doesn't list this as an official charging method.

But considering you charged the JoyCon batteries to 100%, something doesn't add up. You didn't specify the batteries seemed faulty (holding charge for less time than expected), and it would be a bit odd if all of them were improperly calibrated.

 

[Nandru]

Joycons have their own power management circuit, based on the BQ24073 charging IC, as seen in the Charging section of this wiki:

https://retrosix.wiki/wiki/joy-cons-nintendo-switch

I bouch for that info to be mostly correct (the actual ic on my board was a BQ24075) and it helped me locate and diagnose a blown fuse on the battery side.

So, If your joycons arefully charged and still draining the battery, theres a good chance there's an issue around that IC. Maybe a short, a faulty capacitor or a bad IC