|Rechargeable battery packs that don't end up bulging after X years.
Got a loose 3DS XL in need of some repairs for free - Circle Pad broken off, chunk of case plastic missing above the R trigger, seemingly wonky hinges, but functioning perfectly fine; still has a 4 GB SDHC card even. While cleaning it, I noticed that the battery had bulged pretty badly, so I took it out to bring it someplace for recycling. Later on, I remembered that I wanted to try a cartridge on the XL, just to make sure that part works, too. So, I take apart one of my other two, regular 3DS, to check if I can maybe (temporarily) use the battery in the XL... and as it turns out, both of them *also* have bulging batteries, one moreso than the other.
Cue me gathering my other Nintendo handhelds with battery packs like this, to make sure they aren't bulging as well... and as it turns out here, most of them are: the GBA SP's, original DS', DSi XL's, said 3DS' and, of course, the 3DS XL's batteries have all gone bad. All are working, all are original Nintendo ones, but all show the same physical symptoms to some degree. Only the DS Lite and GB micro seem to still have perfectly healthy batteries, despite being much older than, say, the 3DS XL.
So, well, since 1) all these batteries will eventually go bad, bulge or do worse, and 2) Nintendo of Europe doesn't sell original replacement parts anymore *anyway*, I'll be slowly replacing the batteries with 3rd party ones off of Amazon...