Power level misreading, runs for about an hour on "critical battery"

This has been an issue since i bought it at release but i wasn't aware it was an issue back then since there was no way to see the reported battery percentage on stock firmware, so i was just confused that it would run for over an hour on "critical battery level" back then. Now with custom firmware (meaning i can see the reported battery percentage and voltage) and a new (1200mah) battery, it will last for about 3½ hour, with the last hour being on the last 4% (the critical battery level starts at 5%), it will discharge down to 5% at a slightly increasing rate, then at a decreasing rate down to 3%, where it will sit for over 40 minutes.

Looking at the voltage graph, it decrease quickly from about 4V (soon after unplugging, when charging it peaks at about 4,1V) down to the rated 3,7V before it flattens out and very slowly decrease between 1% and 20%, it stays at 3% between 3,2V and 3,45V, before rapidly losing voltage after 3,15V and shutting itself down at 3.0V.

My friend that bought their N3DS at the same time and place as me have the same issue but also didn't realize it was an issue. Both our N3DS batteries have since died and both our new batteries behave the same, making me believe we both got the same faulty batch, so my question is, could replacing the power circuitry fix this? And if likely, where can i find such a replacement?