PSR 740 do not have internal batteries C type in order it works with inside batteries. So, as it works with 10 to 12 Volt we can use an external battery to play the keyboard. Now the question: Has 740 some internal small battery to maintain the data? I think so, because at mine, I take out the jack of power supply during some days and the data do not desappear. The manual it is not clear about this point, but surely there is a backup battery as others keyboards.