I have several question that need clarification here, i have a device draining about 26mA and is using a 9V(rectangular type-NiMh if i am not mistaken) battery regulated at 5V and it could only last for 2 hours before it gave up.

Upon researching on the internet, i found that typical 9V battery carries only around 175mAH (i do not know exactly how much mAH my battery carries)if not lower as opposed to the higher mAH capacity offered by AA and AAA batteries. My question here is:

1. Can i use 4xAA/AAA battery and still get longer operating time compared to a single 9V battery(despite the lower nominal voltage at 6V)? I am trying to minimize the size of the battery used and the biggest prefereble size is the 9V battery mentioned. Button cells is out of question because of their tiny mAH while AA/AAA/B/C/D carries larger mAH but they have very low voltage.

2. How does mAH works in a parallel/series circuit? Does the mAH in all the cells adds up?

I do not have much experience in dealing with batteries so i need some help and suggestion. Thank you very much!

Note - The best battery choice would be those that is easily and commonly available and affordable. Lithium battery is to be avoided if possible because they are expensive.