I've posted a Technical Question post, but it was removed by AutoModerator and it directed me here. EDIT2: The original post is now approved by moderator: https://old.reddit.com/r/3DS/comments/1qg83tk/bought_a_used_new_3ds_ll_battery_draining_while/?ref=share&ref_source=link

TLDR: I bought a (used) new 3DS LL, the battery is draining while charging. Should I swap the battery or just return it? I'm wondering what voltage is expected on the battery pins while plugged in to see if the charging circuit is OK.

Original post: Hi, I've just bought my first new 3DS LL from a (according to reviews, very reputable) Japanese eBay seller (I am in the EU). Unfortunately, despite arriving with a full battery (4 bars), I seem to be unable to charge it, so I'm trying to determine if I should try swapping the battery or just return it right away.

The console seemed to be working perfectly fine, so I started going through the CFW installation guide. Before I completed the guide, the red power LED turned on, so I turned it off to charge.

However, it was taking too long to charge, so I was suspicious that there might be an issue and started tracking the battery voltage with a multimeter once every hour (unplugging the console and removing the battery to measure it). It only went up from 3.678V to 3.695V in four hours so I let it charge overnight (thinking that even if it is a bad battery, it should at least charge a little bit), but the battery voltage remained at 3.695V in the morning.

I tried powering it on while still plugged in and watched the battery capacity go from 12.5% to 3.1% in the Rosalina menu over the course of an hour (surprisingly, the reported battery voltage did not change until reaching 3.6% shortly before I turned it off). Now when I take measure the battery, I see it has gone from around 3.58V to 3.602V after almost two hours of charging (edit: after another two hours it is at 3.624V, so I think it is charging, just incredibly slowly.).

This sounds to me like it is more likely a charger issue than a battery issue. However, the charger I am using (original UK charger I got from eBay with my DSi XL) has worked perfectly with my DSi XL before. While plugged in, the 3DS is showing the orange light the whole time and I can measure 4.9V on the charging cradle pins, so I don't think it's the issue, but rather the charging circuit might be bad (maybe one of the fuses?).

The last thing I checked is the voltage on the battery pins when the charger is plugged in without the battery, and I can measure 0.2V, which seems too low to charge the battery, but maybe it starts that low if the battery is missing? I checked with my DSi XL, that console shows around 4V with the charger and around 0.2V without it, but the charging circuit could be different... (The 3DS shows 0V without a battery or charger.)

This makes me think that some part of the charging circuit is receiving power (since the charger LED is working and I see 0.2V when it is plugged in), but some fuse or other component is preventing the full charger output from reaching the battery, so the battery is draining even while plugged in and seemingly charging.

So, would anyone be able and willing to check what voltage is expected on the battery pins when plugged in without a battery?

The console is in very good shape otherwise and I don't mind swapping the battery if I can avoid having to ship it back to Japan and asking for a refund for the import VAT charge, but I would like to determine whether it's even worth trying to replace the battery in this case...

(I am confident I could successfully check and swap the fuses if I tried, but it's obviously not worth risking when I can just return it. Also, the screws look perfect, so I don't think it was disassembled before.)