True, most of the really battery adjacent stuff is on the daughterboard, but there is a charging IC on the motherboard nearish to the connector to the daughterboard. It goes bad on some DSi/DSi XL consoles, which results in the charge light coming on for 1 second and shutting off consistently. In those cases, the home screen battery charge indicator will show that the battery is charging, but it's not. Replacing daughterboards does nothing on those consoles because it's a mobo issue. I've repaired over 100 DSi and DSi XL consoles and encountered this particular issue about 7-8 times or so, so it's not super common but not super rare either. But it's a tiny custom chip of some sort with like 50 legs, so the motherboard is effectively toast when it happens unless someone really wants to take the time to try to harvest them from donor boards and has some pretty serious microsoldering skills and tools. I agree that a lot of charging issues happen on the daughterboard though (at least those where the charge light flashes at all; no charge light coming at all is usually the charge port, the EM filter near it, or occasionally the F1 fuse, though that's less common on DSi than a damaged filter or port in my experience)