I'm going to try and build my own batteery pack for a portable speaker. It uses 20 volts and 3ampere as input and I realize i will burn through quite a few batteries if trying to power it will just AA or even D type batteries. thats not a problem, the problem is that I'm a bit rusty when it comes to my electrical knowlegde.

What i would like to know is if i need some kind of regulator for something like this, or if it's enought just to keep below the 20volts and the device will automatically draw the right amount of amperes?  This would mean that I could connect thirteen 1,5volt batteries in serial to get roughly 19.5 volts out.  or do I also need to paralell connect those 13 to get the right amperes?


So, for you TL;DR people out there:

How would i connect AA or D batteries (serial/parallel) to power my 20v/3amp device?
Do I need some regulator type device for it, or is it save if keept below those values?
If i need some regulator/other for my desired setup, what can you recommend thats suitable for my situation?

Thanks in advance!