Hi, check this figure. For the randomly turning off issue, you may fix it by soldering the anode of the battery to the PCB board anode points (any of these blue circle positions are the same anode if you check it with your multimeter). The electric contact of TI-84 Plus is problematic. Whenever the contact surface area is insufficient or the current demand is large, the calculator circuit will draw electron from the anode material (which is the copper in TI-84 Plus) and rust the anode until the material is consumed and break the contact totally. Hope this will help you. The anode position may different depends on the version. It’s better to check the resistance of the contact points to be 0! Now it’s working perfectly.