Try cleaning battery connectors otherwise you are gonna have to disassemble camera and do a check with multimeter. U can try contacting canon support or Nikon

I don’t own a 3ds but from my research let me suggest a few repairs: 1. try taking out batter and putting back in. 2. Take out ur game cards and memory to prevent damage to them. ( I damaged my ps vita memory card by not doing it) 3. Try cleaning Charging port and battery contacts. 4. Try leaving 3ds on charge overnight 5. Last resort would be to disassemble ur 3ds and check all the components with a multimeter or if u don’t have one try unplugging and repluging all modules and wires and make sure every thing is properly connected i suggest taking a picture of internals before disassembling anything. Hope it helps

If coffee little coffee went in then just put them in a bag with rice or even better silicon bags for 24 hours. But if coffe is visible floating in there then u need to open them up dry with tissue then put them with silicone bags or if u don’t want to open them put them in a little warmer place at 40 Celsius with silicone bags for at least 3 days. Hope it helps

If it is the board that houses storage then yes. Usually storage is on main board with all other vital components such as processors and memory so basically yes it will be bypassed when logic board is replaced.