My SP4 kept getting hot while charging in sleep mode. Thought I had solved the problem by using the power button rather than closing the type cover to put it into sleep mode. Last night I had it turned completely off, woke up this morning to find it so hot that I had to drop the pen. Since it was powered off the fan obviously didn't kick in. I am left thinking my problem is with the battery. I pulled the charger, opened it up, set it standing with the kick stand to allow for more surface area and it started cooling quite quickly but now there is no way I will charge it unless I am right next to it. About 10 years ago I had a laptop battery catch fire 2 weeks before a recall was issued and do not want that to happen again. It's possible I just got a defective battery but it's also possible there was a bad lot of batteries. For those wondering, the charger was not hot.