Estimate current draw for battery replacement
how much current to allow for?


You have to supply more current than the keyboard needs. If you supply the right voltage then the keyboard will draw itself the needed current.

What is important here is to supply it with the right voltage. So 9-12V and also check if DC or AC.


If you supply it with more current then nothing bad will happen.
If you supply it with less current then it will not work, nothing bad happens.
If you supply it with more voltage then it needs you will destroy it. 




If you know, how long did the keyboard last on that batteries, then you can calculate the power consumption based on the D batteries capacity.

I am assuming the capacity of 8000mAh http://en.wikipedia.org/wiki/D_battery

If the keyboard was able to play for 4 hours, then:

8Ah / 4h = 2A

So the average current draw was 2 Amperes. Bare in mind that this is only the average. So you should supply more.