With four batteries, a POL converter, such as ISF0305A or MEE1S0305SC, the output voltage is controlled at 3V. The safest way is to cut off the existing charging cable and connect it to the charger you made. 
USB mobile phone charger with ordinary 5th battery on the line
The picture above is a diagram of the charger. Diode D1 prevents the battery from being reversed and burns the phone. The cost of the board is about 30 yuan.
This solution is faster, its charging speed is slower, and the maximum current is 200mA. You can also use the LM2623 to make a converter yourself, output 5V, current 1000mA, and get the corresponding current charge by the phone itself. 
The replacement bulb lamp is a substitute bulb for the projector. The price of the replacement bulb lamp will be more affordable than the original Projector Lamp, and the average life can reach 3000 hours, which is suitable for basic film and television in daily life. The operation is simple and easy to install.
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