Common Battery errors from the OS (Windows and Mac) are actually caused from the charger, try replacing the charger with a new OEM charger and allow the computer 6+ hours to charge before booting. This may fix your problem.
Do you mean SIM or Mico-SD, i ask because of your reference to storage (higher capacity). If SIM, then you may want to try to OEM unlock (jailbreak) the phone because it may be carrier locked to a specific SIM service. If Micro-SD, try using a PC to format the card in NTFS first, then re-install in the phone while the power is off and then power on.
Its not a default android or Samsung Note 5 file folder. You will likely get a pop-up when trying to delete it saying it is important. Feel free to delete, is likely added by some 3rd party game added or spam from browsing internet.
Sounds like the sub connection to the button may have come loose or broken. This is the actual click button that is behind the one you physically press in. 1. Close the display and turn the computer over. 2. Remove the screw cover located at the center of the base cover. 3. Remove the 9 Screws on the base cover. 4. use a pick to pry the base cover off of the computer, releasing several plastic clips. Once the back cover is off, you will need to remove the battery from the unit. Following the removal of the battery, follow the below steps to remove / reset / replace the power board. Reverse the procedure to re-assemble the PC.