It can be used, but it consumes power very quickly.
The reason is that the voltage of dry batteries is 1.5V. The voltage of three dry batteries is 4.5V. The rated voltage of lithium battery is 3.7V , and it is only 4.2V when fully charged. The voltage is not enough and it consumes power very quickly when used.
Yes, but low voltage will affect sound quality and volume
Buy a power adapter. The power of an electronic keyboard generally does not exceed 20 W. The power is converted from AC to DC and then input into the keyboard. The DC voltage is generally 12V as long as the output voltage is 12V DC and the current is about 2A, it is enough. Pay attention to the polarity of the power supply when plugging in. Nothing else matters. It just depends on the power of the electronic keyboard. Letme give you a formula, voltage * current = power. For example, the power of your electronic keyboard is 10 watts. Then the power of 10 watts divided by the voltage of 12 = 0.83 current. Once you know the current, you can choose the power supply. However, the output current of the power supply should be at least 1/3 higher than the current you calculated.