Help needed with my project.

[Estonian]

G'day all.

I am new to this forum and to most electronic topics also.
While looking up on membrane switches i discovered eevblog has a forum and it seems to be beginner friendly so thought id ask.

I am working on a little project and need some basic questions answered at my current stage, reddit is a shot in the dark and chatGPT only gets me so far.

I will try to give a brief description on my project without overwhelming you all.. just yet.

Function:
   Handheld, battery operated 6 channel power delivery device
   Outputs 12/24v (on toggle)
   Regural use 10(+-5) Amps (1 channel at a time)
   Peaks at 20 Amps
   Remote to toggle channels and general feedback (leds for channel toggled, active or faulty)

Body will be made out of alloy after battery quantity and pcb size is nearly set, currently at 55x55mm tube.

1. Can i get away with linking 6 or even 4 18650 in series and boosting to 24v for a smaller form factor?
   If yes, what do i need to integrate, like overheat protection.
   Criteria:
      No fan to cool down,heat sink at most
      Constant operation time of 10 minutes at ~10 amps
      20 amp peak operation(few minutes?)

2. Best practice to switch between 12 and 24 volts, dual-output load switch?
   Criteria: start up defaults to 12v

3. What initial faults can be seen in my idea sketch, any input/criticism welcome.

I have included basic flow chart to help understand what i am talking about per pcb layout for the main board and remote (not relevant yet)

I tryed to struggle my way trough with my AI helper but i am way in over my head, this is how far i got for 4 batterys (show the math):

The power required would be:
P = V * I = 24 volts * 20 amps = 480 watts

Let's say the converter is 90% efficient:
Actual power required = Desired power / Efficiency = 480 watts / 0.90 = 533.33 watts

Energy per battery = 3.7 volts * 2.5 amp-hours * 0.90 = 8.325 watt-hours
Total energy of 4 batteries = 4 * 8.325 watt-hours = 33.3 watt-hours

Run time = Energy / Power = 33.3 watt-hours / 480 watts = 0.0694 hours = 4.16 minutes

Lets find out how hot it gets:

During the 4-minute run, the total energy loss in the boost converter is:
Energy_loss_converter = Input power * Time = 533.33 watts * 4 minutes * 60 seconds/minute = 127,999.2 joules

The energy consumed by the batteries during the 4-minute run is the same as the energy delivered to the load, which is:
Energy_delivered_to_load = Output power * Time = 480 watts * 4 minutes * 60 seconds/minute = 115,200 joules

Total_heat_generated = Energy_loss_converter + Energy_delivered_to_load
= 127,999.2 joules + 115,200 joules
= 243,199.2 joules

To convert that in actual degrees i would need the mass of the boost converter, batteries, and any other components which is impossible at this moment and i am sure one of you guys can instantly tell me if these number are ready to explode or safe to sleep next to.

Thank you all who got this far!

[m k]

How much current you can take out of a cell?

If you can take 20A you need 27.5V for 550W.
Eventually the thing will also warm up a bit.

If you boost voltage to double you amps drop to half, but only for output.