I thank you for your time and help. Sometimes is difficult to keep the post short and objective. I will try to clarify some of your presented points.
That's not monitoring anything, it's just saying that during power on, you can set a delay to give power time to stabilize.
I'm not saying it is monitoring. Datasheet is...
ATmega48A/PA/88A/PA/168A/PA/328/P has an On-chip Brown-out Detection (BOD) circuit for monitoring the V CC level during operation by comparing it to a fixed trigger level.
11.5 Brown-out Detection - Pg.49
The voltage level has the clear objective to keep it working nicely, it is presented in the datasheet. To be more specific, the clock source. If the voltage is too low, the clock source is bad and the instructions as well. As I mentioned, what I want to do is hack the chip. Disable initial checks, boost the voltage at a minimum voltage. After that, in code, active BOD, time delay, increase clock frequency and etc...
If you put 2 batteries in series to get twice as much voltage,...
I'm really sorry, but I don't know where I wrote that I need more voltage.
If you read carefully my post, I wrote:
Since my system uses lot of current for the heater, it is preferable to stack all them in parallel.
If you look for any AA batery datasheet, you will see that it has a maximum short current capability. Putting them in series will not increase that capability. However, in parallel they are able to drive more current. If it is not clear, lets make an assumption: Think of a battery as an equivalent Thevenin. It has an internal resistance and a voltage source. If you put in series, you will reduce its current capability due internal resistance voltage drop for a constant resistive load. if you put in parallel. What happens?
My daughter (baby) is suffering from colics. The heater is for her belly and to keep the temperature constant. Thus I built a heater with Ni-Cr wire. I took care to keep the resistance lower as possible R=0.5ohm. With that design I am able to put 3,4,5... AA rechargeable batteries in parallel to run all over the night.
I think communication is complicated. I'm not a native English speaker, which difficult it. Please, be more patient...