santtu

I think that the battery-chamber latch hits the sealing, if battery is accidentally inserted upside down or backwards and trying to close the cover. Possible cause / explanation?

Why?

Ken Rockwell uses Nikon D3300 and his recommended settings is JPEG BASIC and image size SMALL (6Mpix) because "The default of JPEG Normal wastes twice as much space in your computer" and "Since the pictures look the same at BASIC, I use it so more pictures fit on my card, and more importantly, I don't clog up my computer and everything transfers, copies and sends twice as fast." and "I'm serious: even at the Small setting you've got 6 very sharp megapixels, which is more than enough to print at any size if your photo is in focus in the first place." He also said "The NORMAL, FINE and NEF RAW modes are for people who don't mind fitting only 12 images on a card. The pictures really do look the same; try it and see if you're curious. I did, which is why I shoot JPG BASIC." So, it is the same that I will say that my doctor is not "pro", I can choose my medicine myself!

I had several freezes with two sandisk extreme 32GB 90MB/s card

That's right

Yes. Also works with just one battery.

Shutter AE setting is off? Shutter AE off, Aperture Priority and Auto-ISO, shutter speed is not showing. There is no solution AFAIK, need to set ISO or shutter speed manually.