I want to keep my 3DS in the charging cradle for I can get updates with Spotpass. I am worried that it will mess up its bettery life though.

Has anybody tested this out?

I don't think it would be any worse than a PSP or Xbox Controller. The 3DS stops charging when it's fully charged, just like those devices. I don't think you have to worry about overcharging it like you would a Wii Remote charging station.

But I could be wrong.

The cradle is fine, no need to worry. The way the 3DS battery and charging system is designed it basically has no memory. It will wear down over the years (entropy always wins in the end) but charging it won't impact it.

I know that if I charge it only when its dying then it won't kill the battery.

If I play it for 20 minutes and put it back on the charging cradle and it still has nearly all of its battery life left...it won't mess up the battery because its only charging to get those 20 minutes back?

The main question is: If I leave my 3DS on WIFi mode, in sleep mode 24 hours a day in its charging cradle(Besides for when I am playing it) will it kill the battery memory? 

No memory problem. The 3DS battery is basically immune to memory problems (it will get a little, tiny bit, after years of doing that every day you may lose a few percent of battery life). A lot of newer cell phones use the same system. No need to worry at all.

Really? Alright, thanks a lot! I will be leaving my 3DS in its cradle from now on then LOL

I hadn't heard of having to discharge battery nowadays.