I need to run a pump (drawing 95mA at peak flowrate) at +14V and the rest of my circuit runs on +3.3V.
To save on battery costs, I was thinking of purchasing four 18650s at 3.6V 3500mAh per cell and stacking them in series to produce ~14.4V needed for the pump (it can run between 10-15V and we are going to use PWM to control the voltage i.e. the flowrate).
Could I also run two terminals from one cell (at 3.6V) and regulate that to 3.3V for my lower voltage loads? I understand that this will cause one of the four cells to discharge faster than the other three, but I plan on using a BQ29209 balancing chip to maximize the capacity I can get out of them.
Would it be wiser to just use two buck converters from 14.4V down to 12V and 3.3V respectively?
Ideally, if I had more money, I would put 4x 3.6V in series = 14.4V @ 3500mAh, and then another 2x 3.6V in parallel = 3.6V @ 7000mAh to get more capacity.